Multistage semiconductor quantum detector circuit incorporating anticorrelation

ABSTRACT

A novel and useful multistage semiconductor quantum detector circuit incorporating an anticorrelation mechanism. The quantum structure has at least the first stage sensor of the detector merged into the quantum structure in order to minimize loading of the quantum structure. The merged quantum structure and detector sensor may be encapsulated in a metal cage in order to provide enhanced rejection of the environmental parasitic electric and/or magnetic fields. A double boot strapping detector front-end configuration substantially eliminates the loading coming from both the gate-source and the gate-drain parasitic capacitances of the first sensor device of the detector that is connected to the quantum structure. In addition, differential detection aids in rejecting leakage, noise, and correlated interference coupling. Both dummy referenced differential detection as well as self-referenced differential detection may be employed in the detector. Moreover, correlated double sampling is used after preamplification in the detector in order to further reject noise and perturbations in the system.

REFERENCE TO PRIORITY APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.16/445,645, filed Jun. 19, 2019, entitled “Semiconductor ControlledQuantum Interaction Gates,” which claims the benefit of U.S. ProvisionalApplication No. 62/687,800, filed Jun. 20, 2018, entitled “ElectricSignal Pulse-Width And Amplitude Controlled And Re-ProgrammableSemiconductor Quantum Rotation Gates,” U.S. Provisional Application No.62/687,803, filed Jun. 21, 2018, entitled “Semiconductor QuantumStructures and Computing Circuits Using Local Depleted Well Tunneling,”U.S. Provisional Application No. 62/689,100, filed Jun. 23, 2018,entitled “Semiconductor Controlled Entangled-Aperture-Logic QuantumShift Register,” U.S. Provisional Application No. 62/694,022, filed Jul.5, 2018, entitled “Double-V Semiconductor Entangled-Aperture-LogicParallel Quantum Interaction Path,” U.S. Provisional Application No.62/687,779, filed Jun. 20, 2018, entitled “Semiconductor QuantumStructures And Gates Using Through-Thin-Oxide Well-To-Gate ApertureTunneling,” U.S. Provisional Application No. 62/687,793, filed Jun. 20,2018, entitled “Controlled Semiconductor Quantum Structures AndComputing Circuits Using Aperture Well-To-Gate Tunneling,” U.S.Provisional Application No. 62/688,341, filed Jun. 21, 2018, entitled“3D Semiconductor Quantum Structures And Computing Circuits UsingFin-To-Gate Tunneling,” U.S. Provisional Application No. 62/689,035,filed Jun. 22, 2018, entitled “3D Semiconductor Quantum Structures AndComputing Circuits Using Controlled Tunneling Through Local FinDepletion Regions,” U.S. Provisional Application No. 62/689,291, filedJun. 25, 2018, entitled “Semiconductor Quantum Dot And Qubit StructuresUsing Aperture-Tunneling Through Oxide Layer,” U.S. ProvisionalApplication No. 62/689,166, filed Jun. 24, 2018, entitled “SemiconductorEntangled-Aperture-Logic Quantum Ancillary Gates,” U.S. ProvisionalApplication No. 62/692,745, filed Jun. 20, 2018, entitled“Re-Programmable And Re-Configurable Quantum Processor Using Pulse-WidthBased Rotation Selection And Path Access Or Bifurcation Control,” U.S.Provisional Application No. 62/692,804, filed Jul. 1, 2018, entitled“Quantum Processor With Dual-Path Quantum Error Correction,” U.S.Provisional Application No. 62/692,844, filed Jul. 1, 2018, entitled“Quantum Computing Machine With Partial Data Readout And Re-InjectionInto The Quantum State,” U.S. Provisional Application No. 62/726,290,filed Jun. 20, 2018, entitled “Controlled-NOT and Tofolli SemiconductorEntangled-Aperture-Logic Quantum Gates,” U.S. Provisional ApplicationNo. 62/695,842, filed Jul. 10, 2018, entitled “Entangled Aperture-LogicSemiconductor Quantum Computing Structure with Intermediary InteractorPath,” U.S. Provisional Application No. 62/698,278, filed Jul. 15, 2018,entitled “Entangled Aperture-Logic Semiconductor Quantum Bifurcation andMerging Gate,” U.S. Provisional Application No. 62/726,397, filed Sep.3, 2018, entitled “Semiconductor Quantum Structure With SimultaneousShift Into Entangled State,” U.S. Provisional Application No.62/791,818, filed Jan. 13, 2019, entitled “Semiconductor Process forQuantum Structures with Staircase Active Well,” U.S. ProvisionalApplication No. 62/788,865, filed Jan. 6, 2018, entitled “SemiconductorProcess For Quantum Structures Without Inner Contacts And DopingLayers,” U.S. Provisional Application No. 62/794,591, filed Jan. 19,2019, entitled “Semiconductor Quantum Structures Using LocalizedAperture Channel Tunneling Through Controlled Depletion Region,” U.S.Provisional Application No. 62/703,888, filed Jul. 27, 2018, entitled“Aperture Tunneling Semiconductor Quantum Dots and Chord-Line QuantumComputing Structures,” U.S. Provisional Application No. 62/726,271,filed Sep. 2, 2018, entitled “Controlled Local Thermal Activation OfFreeze-Out Semiconductor Circuits For Cryogenic Operation,” U.S.Provisional Application No. 62/731,810, filed Sep. 14, 2018, entitled“Multi-Stage Semiconductor Quantum Detector with Anti-Correlation MergedWith Quantum Core,” and U.S. Provisional Application No. 62/794,655,filed Jan. 20, 2019, entitled “Semiconductor Quantum Structures UsingPreferential Tunneling Direction Through Thin Insulator Layers.” All ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The subject matter disclosed herein relates to the field of quantumcomputing and more particularly relates to a multistage semiconductorquantum detector circuit incorporating anticorrelation.

BACKGROUND OF THE INVENTION

Quantum computers are machines that perform computations using thequantum effects between elementary particles, e.g., electrons, holes,ions, photons, atoms, molecules, etc. Quantum computing utilizesquantum-mechanical phenomena such as superposition and entanglement toperform computation. Quantum computing is fundamentally linked to thesuperposition and entanglement effects and the processing of theresulting entanglement states. A quantum computer is used to performsuch computations which can be implemented theoretically or physically.

Currently, analog and digital are the two main approaches to physicallyimplementing a quantum computer. Analog approaches are further dividedinto quantum simulation, quantum annealing, and adiabatic quantumcomputation. Digital quantum computers use quantum logic gates to docomputation. Both approaches use quantum bits referred to as qubits.

Qubits are fundamental to quantum computing and are somewhat analogousto bits in a classical computer. Qubits can be in a |0> or |1> quantumstate but they can also be in a superposition of the |0> and |1> states.When qubits are measured, however, they always yield a |0> or a |1>based on the quantum state they were in.

The key challenge of quantum computing is isolating such microscopicparticles, loading them with the desired information, letting theminteract and then preserving the result of their quantum interaction.This requires relatively good isolation from the outside world and alarge suppression of the noise generated by the particle itself.Therefore, quantum structures and computers operate at very lowtemperatures (e.g., cryogenic), close to the absolute zero kelvin (K),in order to reduce the thermal energy/movement of the particles to wellbelow the energy/movement coming from their desired interaction. Currentphysical quantum computers, however, are very noisy and quantum errorcorrection is commonly applied to compensate for the noise.

Most existing quantum computers use superconducting structures torealize quantum interactions. Their main drawbacks, however, are thefact that superconducting structures are very large and costly and havedifficulty in scaling to quantum processor sizes of thousands ormillions of quantum-bits (qubits). Furthermore, they need to operate atfew tens of milli-kelvin (mK) temperatures, that are difficult toachieve and where it is difficult to dissipate significant power tooperate the quantum machine.

SUMMARY OF THE INVENTION

The following summary is illustrative only and is not intended to belimiting in any way. That is, the following summary is provided tointroduce concepts, highlights, benefits and advantages of the novel andnon-obvious techniques described herein. Select implementations arefurther described below in the detailed description. Thus, the followingsummary is not intended to identify essential features of the claimedsubject matter, nor is it intended for use in determining the scope ofthe claimed subject matter.

The present invention is a multistage semiconductor quantum detectorcircuit incorporating an anticorrelation mechanism. The quantumstructure has at least the first stage sensor of the detector mergedinto the quantum structure in order to minimize loading of the quantumstructure. The merged quantum structure and detector sensor may beencapsulated in a metal cage in order to provide enhanced rejection ofthe environmental parasitic electric and/or magnetic fields. A doubleboot strapping detector front-end configuration substantially eliminatesthe loading coming from both the gate-source and the gate-drainparasitic capacitances of the first sensor device of the detector thatis connected to the quantum structure. In addition, differentialdetection aids in rejecting leakage, noise, and correlated interferencecoupling. Both dummy referenced differential detection as well asself-referenced differential detection may be employed in the detector.Moreover, correlated double sampling is used after preamplification inthe detector in order to further reject noise and perturbations in thesystem.

In addition, several quantum structures provide various controlfunctions whereby particles are brought into close proximity so they caninteract with one another. Particles relatively far away one from theother have small or negligible interaction. Two or more quantumparticles or states brought in close proximity will interact andexchange information. Such particles are “entangled” as each particlecarries information from all particles that interacted. Afterentanglement, the particles are moved away from each other but theystill carry the information contained initially. Measurement anddetection is performed on the particles from the entangled ensemble todetermine whether the particle is present or not in a given qdot.

A quantum interaction gate is a circuit or structure operating on arelatively small number of qubits. The type of quantum interaction gateis given both by the physical/geometrical structure of the gate and bythe corresponding control signal. A given geometrical structure mayperform different quantum interaction gate functions depending on thecontrol signals applied, including their shape, amplitude, pulse width,duration, position, etc.

Quantum interaction gates implement several quantum functions includinga controlled NOT gate, quantum annealing gate, controlled SWAP gate, acontrolled rotation (i.e. controlled Pauli) gate, and ancillary gate.These quantum interaction gates can have numerous shapes includingdouble V shape, H shape, X shape, L shape, I shape, etc.

Quantum annealing is the operation of finding the minima of a givenfunction over a given set of candidate solutions using the quantumfluctuation method. The SWAP quantum, interaction gate functions topermute the incoming quantum states. The Pauli quantum interaction gateis a single qubit quantum interaction gate that performs rotation aboutthe z, y, and x axis. Ancillary or ancilla qubits have an unknown valuea priori. The Hadamard equal distribution quantum state is an example ofan ancilla qubit.

This, additional, and/or other aspects and/or advantages of theembodiments of the present invention are set forth in the detaileddescription which follows; possibly inferable from the detaileddescription; and/or learnable by practice of the embodiments of thepresent invention.

There is thus provided in accordance with the invention, a quantumdetector coupled to a quantum circuit, comprising a main quantum sensorcoupled to a main semiconductor quantum well whose output is to bedetected for a presence or absence of a particle previously injectedthereto, said main quantum sensor operative to generate a main sensorsignal, a dummy quantum sensor coupled to a dummy semiconductor quantumwell whereby no particle is injected thereto, said dummy quantum sensoroperative to generate a dummy sensor signal, and an amplifier andconditioning circuit operative to detect the presence or absence of saidparticle at the output of said main quantum circuit in accordance with adifference between said main sensor signal and said dummy sensor signal.

There is also provided in accordance with the invention, a quantumdetector coupled to a quantum circuit, comprising a main quantum sensorcoupled to a first end of a semiconductor quantum well and operative togenerate a main sensor signal corresponding to the presence or absenceat said first end of a particle previously injected into saidsemiconductor quantum circuit, a complementary quantum sensor coupled toa second end of the semiconductor quantum well and operative to generatea complementary sensor signal corresponding to the presence or absenceof the particle at said second end, and an amplifier and conditioningcircuit operative to detect the presence or absence of said particle insaid semiconductor quantum well in accordance with a self-referenceddifference between said main sensor signal and said complementary sensorsignal.

There is further provided in accordance with the invention, a quantumdetector, comprising a sensor coupled to a quantum well of asemiconductor quantum circuit and operative to generate a sensor signalcorresponding to the presence or absence of a particle previouslyinjected into said semiconductor quantum circuit, an amplifier andconditioning circuit operative to receive an output of said sensor, saidamplifier and conditioning circuit comprising a preamplifier circuitoperative to convert presence of charge at its input to a voltagesignal, a correlated double sampler (CDS) circuit coupled to saidpreamplifier and operative to further reject noise from said voltagesignal, a post-amplifier circuit coupled to said CDS and operative togenerate a detection output signal from an output of said CDS, and adevice exclusion zone surrounding said quantum circuit and sensor andoperative to isolate said quantum circuit and sensor from said amplifierand conditioning circuit.

There is also provided in accordance with the invention, a method ofdetecting a presence or absence of a particle in a main quantum circuit,comprising first sensing via a first sensor for the presence or absenceof a particle previously injected into a main quantum circuit andgenerating a main sensor signal thereby, second sensing via a secondsensor an absence of a particle in a dummy quantum circuit andgenerating a dummy sensor signal thereby, and generating a detectoroutput in accordance with a difference signal corresponding to adifference between said main sensor signal and said dummy sensor signal.

There is further provided in accordance with the invention, a method ofdetecting a presence or absence of a particle in a main quantum circuit,comprising first sensing via a first sensor at one end of a quantumcircuit for the presence or absence of a particle previously injectedtherein and generating a first sensor signal thereby, second sensing viaa second complementary sensor at a second end of the quantum circuit forthe presence or absence of a particle and generating a complementarysecond sensor signal thereby, and generating a detector output inaccordance with a difference signal corresponding to a differencebetween said first sensor signal and said complementary second sensorsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail in the followingexemplary embodiments and with reference to the figures, where identicalor similar elements may be partly indicated by the same or similarreference numerals, and the features of various exemplary embodimentsbeing combinable. The invention is herein described, by way of exampleonly, with reference to the accompanying drawings, wherein:

FIG. 1 is a high level block diagram illustrating an example quantumcomputer system constructed in accordance with the present invention;

FIG. 2 is a high level block diagram illustrating a quantum structureand its interface using integrated electronic control circuitry;

FIG. 3A is a diagram illustrating a quantum structure beforeinitialization;

FIG. 3B is a diagram illustrating an example ideal and decoherence Rabioscillation waveform;

FIG. 3C is a diagram illustrating a quantum structure initialized to afirst base state;

FIG. 3D is a diagram illustrating an example Rabi oscillation waveformat initialization;

FIG. 3E is a diagram illustrating a quantum structure initialized to asecond base state;

FIG. 3F is a diagram illustrating an example waveform having half theRabi oscillation period;

FIG. 3G is a diagram illustrating a quantum structure with a particle intwo qdots at the same time;

FIG. 3H is a diagram illustrating an example waveform having one quarterthe Rabi oscillation period;

FIG. 3I is a diagram illustrating a first quantum structure with aparticle split between two qdots at the same time;

FIG. 3J is a diagram illustrating an example waveform having a periodless than one quarter the Rabi oscillation period;

FIG. 3K is a diagram illustrating a second quantum structure with aparticle split between two qdots at the same time;

FIG. 3L is a diagram illustrating an example waveform having a periodmore than one quarter the Rabi oscillation period;

FIG. 4A is a diagram illustrating a circular shaped quantum structureincorporating local depleted well tunneling;

FIG. 4B is a diagram illustrating the change in the aperture tunnelbarrier from a wide depletion region to a narrow depletion region;

FIG. 4C is a diagram illustrating a first rectangular shaped quantumstructure incorporating local depleted well tunneling;

FIG. 4D is a diagram illustrating the change in the aperture tunnelbarrier from a wide depletion region to a narrow depletion region;

FIG. 5 is a diagram illustrating a second rectangular shaped quantumstructure incorporating local depleted well tunneling;

FIG. 6 is a diagram illustrating a cross section of an example quantumstructure;

FIG. 7A is a diagram illustrating an example circular shape for thequantum structure of the present invention;

FIG. 7B is a diagram illustrating an example square shape for thequantum structure of the present invention;

FIG. 7C is a diagram illustrating an example square shape with roundedcorners for the quantum structure of the present invention;

FIG. 7D is a diagram illustrating an example hexagonal shape for thequantum structure of the present invention;

FIG. 7E is a diagram illustrating an example rectangular shape for thequantum structure of the present invention;

FIG. 7F is a diagram illustrating an example trapezoidal shape for thequantum structure of the present invention;

FIG. 7G is a diagram illustrating a first example overlapping squareshape for the quantum structure of the present invention;

FIG. 7H is a diagram illustrating a first example ‘L’ shape for thequantum structure of the present invention;

FIG. 7I is a diagram illustrating an example ‘Z’ shape for the quantumstructure of the present invention;

FIG. 7J is a diagram illustrating a second example ‘L’ shape for thequantum structure of the present invention;

FIG. 7K is a diagram illustrating an example barely touching squareshape for the quantum structure of the present invention;

FIG. 7L is a diagram illustrating an example barely touching squareshape with optical proximity control for the quantum structure of thepresent invention;

FIG. 7M is a diagram illustrating an example double square with narrowneck shape for the quantum structure of the present invention;

FIG. 7N is a diagram illustrating a second example overlapping squareshape for the quantum structure of the present invention;

FIG. 7O is a diagram illustrating a third example overlapping squareshape for the quantum structure of the present invention;

FIG. 7P is a diagram illustrating an example barely touching rectangularshape for the quantum structure of the present invention;

FIG. 7Q is a diagram illustrating an example barely touching doubleoverlapping square shape for the quantum structure of the presentinvention;

FIG. 7R is a diagram illustrating an example double square connected viasingle smaller square shape for the quantum structure of the presentinvention;

FIG. 7S is a diagram illustrating an example double square connected viadouble smaller square shape for the quantum structure of the presentinvention;

FIG. 8A is a diagram illustrating a first example control gate for thequantum structure of the present invention;

FIG. 8B is a diagram illustrating a second example control gate for thequantum structure of the present invention;

FIG. 8C is a diagram illustrating a third example control gate for thequantum structure of the present invention;

FIG. 9A is a diagram illustrating an example quantum structure withdouble square shape;

FIG. 9B is a diagram illustrating an example quantum structure withdouble square shape and optical proximity control;

FIG. 9C is a diagram illustrating an example quantum structure withdouble square and narrow neck shape;

FIG. 9D is a diagram illustrating a first example quantum structure withdouble overlapping square shape;

FIG. 9E is a diagram illustrating a second example quantum structurewith double overlapping square shape;

FIG. 9F is a diagram illustrating an example quantum structure with ‘L’shape;

FIG. 9G is a diagram illustrating an example quantum structure withdouble rounded barely touching square shape;

FIG. 9H is a diagram illustrating an example quantum structure withdouble rectangular shape;

FIG. 9I is a diagram illustrating an example quantum structure withdouble square connected via double smaller square shape;

FIG. 9J is a diagram illustrating an example quantum structure withdouble rounded square with narrow neck shape;

FIG. 9K is a diagram illustrating an example quantum structure with anoverlapping pair of double rounded squares with narrow neck shape;

FIG. 9L is a diagram illustrating a first example quantum structure witha pair of barely touching double overlapping square shape;

FIG. 9M is a diagram illustrating a second example quantum structurewith a pair of barely touching double overlapping square shape;

FIG. 9N is a diagram illustrating a first example quantum structure witha double square shape with narrow neck and butterfly shaped controlgate;

FIG. 9O is a diagram illustrating a second example quantum structurewith a double square shape with narrow neck and butterfly shaped controlgate;

FIG. 9P is a diagram illustrating an example quantum structure with apair of overlapping double square shapes with narrow neck and butterflyshaped control gates;

FIG. 9Q is a diagram illustrating an example conventional FET with drainand source doped diffusion and contacts;

FIG. 9R is a diagram illustrating an example half conventional FET andhalf quantum structure;

FIG. 9S is a diagram illustrating an example quantum structure withrectangular shaped wells;

FIG. 9T is a diagram illustrating an example quantum structure withdissimilar rectangular shaped wells;

FIG. 9U is a diagram illustrating an example quantum structure withoffset rectangular shaped wells;

FIG. 9V is a diagram illustrating a first example quantum structure withspaced apart rectangular shaped wells;

FIG. 9W is a diagram illustrating a first example quantum structure withspaced apart rectangular shaped wells offset from each other;

FIG. 9X is a diagram illustrating a second example quantum structurewith spaced apart rectangular shaped wells;

FIG. 9Y is a diagram illustrating a second example quantum structurewith spaced apart rectangular shaped wells offset from each other;

FIG. 9Z is a diagram illustrating a third example quantum structure withspaced apart rectangular shaped wells offset from each other;

FIG. 9AA is a diagram illustrating a fourth example quantum structurewith spaced apart rectangular shaped wells offset from each other;

FIG. 9AB is a diagram illustrating a first example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AC is a diagram illustrating a second example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AD is a diagram illustrating a third example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AE is a diagram illustrating a fourth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AF is a diagram illustrating a fifth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AG is a diagram illustrating a sixth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 10A is a diagram illustrating a first example interface device ofthe present invention in more detail;

FIG. 10B is a diagram illustrating a second example interface device ofthe present invention;

FIG. 10C is a diagram illustrating a third example interface device ofthe present invention;

FIG. 11 is a diagram illustrating a cross section of a first examplequantum structure and conventional FET;

FIG. 12 is a diagram illustrating a cross section of a second examplequantum structure and conventional FET;

FIG. 13 is a diagram illustrating a cross section of a third examplequantum structure and conventional FET;

FIG. 14 is a diagram illustrating an example quantum structure withinterface devices;

FIG. 15A is a diagram illustrating a first example multiple qdot quantumstructure with interface devices on either end thereof;

FIG. 15B is a diagram illustrating an example layout of an examplequantum structure;

FIG. 16 is a diagram illustrating a cross section of the quantumstructure of FIG. 15A;

FIG. 17A is a diagram illustrating the aperture tunnel barrier for a twoquantum dot structure;

FIG. 17B is a diagram illustrating a first example change in theaperture tunnel barrier for the two quantum dot structure;

FIG. 17C is a diagram illustrating a second example change in theaperture tunnel barrier for the two quantum dot structure;

FIG. 18 is a diagram illustrating an example quantum structuresurrounded by a spin control magnetic coil;

FIG. 19 is a diagram illustrating a second example multiple qdot quantumstructure;

FIG. 20 is a diagram illustrating a third example multiple qdot quantumstructure;

FIG. 21 is a diagram illustrating a fourth example multiple qdot quantumstructure;

FIG. 22A is a diagram illustrating an example floating well detectioncircuit;

FIG. 22B is a diagram illustrating the layout for the example floatingwell detection circuit;

FIG. 22C is a diagram illustrating the cross section for the floatingwell detection circuit;

FIG. 23A is a diagram illustrating an example floating gate detectioncircuit;

FIG. 23B is a diagram illustrating the layout for the example floatinggate detection circuit;

FIG. 23C is a diagram illustrating the cross section for the floatinggate detection circuit;

FIG. 24 is an example potential diagram for the floating gate detectioncircuit;

FIG. 25 is a diagram illustrating an example 3D semiconductor quantumstructure using fin to fin tunneling through local depletion region;

FIG. 26 is a diagram illustrating a three dimensional view of an example3D semiconductor quantum structure with fin to fin tunneling undercontrol of a control gate;

FIG. 27A is a diagram illustrating a cross section, side view, and topview of an example 3D two qdot quantum structure using local findepletion tunneling;

FIG. 27B is a diagram illustrating a cross section, side views, and topview of an example 3D multiple qdot quantum structure using local findepletion tunneling;

FIG. 28A is a diagram illustrating two example double V fin-gate-finstructures having two wells placed in close proximity allowing quantumparticles to interact;

FIG. 28B is a diagram illustrating an example 3D semiconductor quantumstructure using fin-to-fin tunneling through a local depleted regionwith a shared well between two fin paths providing bifurcation;

FIG. 28C is a diagram illustrating an example quantum structure withdummy gates and gate cuts that separate control and dummy gates;

FIG. 28D is a diagram illustrating an example hybrid planar and 3Dsemiconductor quantum structure using both fin-to-fin and well-to-welltunneling through local depletion region;

FIG. 29 is a diagram illustrating an example 3D semiconductor quantumstructure using fin-to-gate tunneling through oxide;

FIG. 30 is a diagram illustrating a three dimensional view of an example3D semiconductor quantum structure using fin-to-gate and gate-to-fintunneling through oxide;

FIG. 31 is a diagram illustrating a cross section, side view, and topview of an example 3D semiconductor quantum structure using fin-to-gatetunneling through oxide;

FIG. 32 is a diagram illustrating a cross section of an example 3Dsemiconductor quantum structure using fin-to-gate and gate-to-fintunneling;

FIG. 33 is a diagram illustrating a top view of an example two qdot 3Dsemiconductor quantum structure using fin-to-gate tunneling throughoxide;

FIG. 34A is a diagram illustrating an example double V quantuminteraction structure using 3D semiconductor process with fin-to-gatetunneling;

FIG. 34B is a diagram illustrating an example quantum structure withfin-to-gate tunneling with dummy gates and cuts to create dummy fins;

FIG. 34C is a diagram illustrating an example hybrid planar and 3Dsemiconductor quantum structure using both fin-to-gate and well-to-gatetunneling;

FIG. 35 is a diagram illustrating an example initializationconfiguration for a quantum interaction structure using tunnelingthrough gate-well oxide layer;

FIG. 36 is a diagram illustrating an example initializationconfiguration for a quantum interaction structure using tunnelingthrough local depleted region in a continuous well;

FIG. 37A is a diagram illustrating an example planar semiconductorquantum structure using tunneling through oxide layer;

FIG. 37B is a diagram illustrating an example planar semiconductorquantum structure using tunneling through local depleted well;

FIG. 37C is a diagram illustrating an example 3D process semiconductorquantum structure using tunneling through oxide layer;

FIG. 37D is a diagram illustrating an example 3D process semiconductorquantum structure using tunneling through local depleted well;

FIG. 38A is a diagram illustrating an example CNOT quantum interactiongate using tunneling through oxide layer implemented in planarsemiconductor processes;

FIG. 38B is a diagram illustrating an example CNOT quantum interactiongate using tunneling through local depleted well implemented in planarsemiconductor processes;

FIG. 38C is a diagram illustrating an example CNOT quantum interactiongate using tunneling through oxide layer implemented in 3D semiconductorprocesses;

FIG. 38D is a diagram illustrating an example CNOT quantum interactiongate using tunneling through local depleted fin implemented in 3Dsemiconductor processes;

FIG. 39A is a diagram illustrating a first example controlled NOT doublequbit structure and related Rabi oscillation;

FIG. 39B is a diagram illustrating a second example controlled NOTdouble qubit structure and related Rabi oscillation;

FIG. 39C is a diagram illustrating a third example controlled NOT doublequbit structure and related Rabi oscillation;

FIG. 39D is a diagram illustrating a fourth example controlled NOTdouble qubit structure and related Rabi oscillation;

FIG. 40 is a diagram illustrating a controlled NOT quantum interactiongate for several control and target qubit states;

FIG. 41A is a diagram illustrating an example controlled NOT quantuminteraction gate using square layers with partial overlap;

FIG. 41B is a diagram illustrating an example Toffoli quantuminteraction gate using square layers with partial overlap;

FIG. 41C is a diagram illustrating an example higher order controlledNOT quantum interaction gate using square layers with partial overlap;

FIG. 42A is a diagram illustrating a first example of semiconductorentanglement quantum interaction gate including initialization, staging,interaction, and output locations;

FIG. 42B is a diagram illustrating a second example of semiconductorentanglement quantum interaction gate including initialization, staging,interaction, and output locations;

FIG. 42C is a diagram illustrating a third example of semiconductorentanglement quantum interaction gate including initialization, staging,interaction, and output locations;

FIG. 42D is a diagram illustrating a fourth example of semiconductorentanglement quantum interaction gate including initialization, staging,interaction, and output locations;

FIG. 43A is a diagram illustrating an example quantum interaction gateusing double V interaction between neighboring paths;

FIG. 43B is a diagram illustrating an example quantum interaction gateusing H interaction between neighboring paths;

FIG. 43C is a diagram illustrating an example quantum interaction ringwith star shaped access and double V interaction with multiple next doorneighbors;

FIG. 43D is a diagram illustrating an example quantum interaction ringwith star shaped access and H interaction with multiple next doorneighbors;

FIG. 44A is a diagram illustrating an example T shape quantuminteraction gate using tunneling through a local depleted well forinteraction between two qubits;

FIG. 44B is a diagram illustrating an example H shape quantuminteraction gate using tunneling through a local depleted well forinteraction between two qubits;

FIG. 44C is a diagram illustrating an example of a triple V shapequantum interaction gate using tunneling through a local depleted wellfor interaction between three qubits;

FIG. 44D is a diagram illustrating an example double V shape quantuminteraction gate using tunneling through a local depleted well forinteraction between two qubits;

FIG. 45A is a diagram illustrating a first example CNOT quantuminteraction gate within a grid array of programmable semiconductorqubits;

FIG. 45B is a diagram illustrating a second example CNOT quantuminteraction gate within a grid array of programmable semiconductorqubits;

FIG. 46 is a diagram illustrating an example quantum interaction gateconstructed with both electric and magnetic control;

FIG. 47 is a diagram illustrating an example grid array of programmablesemiconductor qubits with both global and local magnetic;

FIG. 48A is a diagram illustrating a first stage of an example quantuminteraction gate particle interaction;

FIG. 48B is a diagram illustrating a second stage of an example quantuminteraction gate particle interaction;

FIG. 48C is a diagram illustrating a third stage of an example quantuminteraction gate particle interaction;

FIG. 48D is a diagram illustrating a fourth stage of an example quantuminteraction gate particle interaction;

FIG. 48E is a diagram illustrating a fifth stage of an example quantuminteraction gate particle interaction;

FIG. 48F is a diagram illustrating a sixth stage of an example quantuminteraction gate particle interaction;

FIG. 48G is a diagram illustrating a seventh stage of an example quantuminteraction gate particle interaction;

FIG. 48H is a diagram illustrating an eighth stage of an example quantuminteraction gate particle interaction;

FIG. 49A is a diagram illustrating an example semiconductor qubit usingtunneling through a separate layer planar structure;

FIG. 49B is a diagram illustrating an example semiconductor qubit usingtunneling through a local depleted well planar structure;

FIG. 49C is a diagram illustrating an example semiconductor qubit usingtunneling through a separate layer 3D FIN-FET structure;

FIG. 49D is a diagram illustrating an example semiconductor qubit usingtunneling through a local depleted well 3D FIN-FET structure;

FIG. 49E is a diagram illustrating a semiconductor CNOT quantuminteraction gate using two qubit double qdot structures with tunnelingthrough a separate structure planar structure;

FIG. 49F is a diagram illustrating a first example quantum interactiongate with interaction between two particles in the same continuous well;

FIG. 49G is a diagram illustrating a second example quantum interactiongate with interaction between two particles in the same continuous well;

FIG. 49H is a diagram illustrating a third example quantum interactiongate with interaction between two particles in the same continuous well;

FIG. 49I is a diagram illustrating a first example quantum interactiongate with interaction between two particles in different continuouswells;

FIG. 49J is a diagram illustrating a second example quantum interactiongate with interaction between two particles in different continuouswells;

FIG. 49K is a diagram illustrating a second example quantum interactiongate with interaction between two particles in different continuouswells;

FIG. 49L is a diagram illustrating a second example quantum interactiongate with interaction between two particles in different continuouswells;

FIG. 50A is a diagram illustrating a CNOT quantum interaction gate usingtwo qubit double qdot structures with tunneling through a separatestructure planar structure with gating to classic circuits;

FIG. 50B is a diagram illustrating a CNOT quantum interaction gate withtunneling through a local depleted well using voltage driven gateimposing and gating to classic circuits;

FIG. 50C is a diagram illustrating a CNOT quantum interaction gate withtunneling through a local depleted well using voltage driven gateimposing and multiple gating to classic circuits;

FIG. 50D is a diagram illustrating an example quantum interaction gatewith continuous well incorporating reset, inject, impose, and detectcircuitry;

FIG. 51A is a diagram illustrating an example double V CNOT quantuminteraction gate using separate control gates that mandates largerspacing resulting in a weaker interaction;

FIG. 51B is a diagram illustrating an example double V CNOT quantuminteraction gate using common control gates for sections in closerproximity to permit smaller spacing and stronger interaction;

FIG. 51C is a diagram illustrating an example double V CNOT quantuminteraction gate using common control gates for two control gates onboth sides of the interacting qdots;

FIG. 51D is a diagram illustrating an example double V CNOT quantuminteraction gate incorporating inject, impose, and detect circuitry;

FIG. 52A is a diagram illustrating a first example z shift registerquantum interaction gate using planar process with partial overlap ofsemiconductor well and control gate;

FIG. 52B is a diagram illustrating a second example z shift registerquantum interaction gate using planar process with partial overlap ofsemiconductor well and control gate;

FIG. 52C is a diagram illustrating an example of H-style quantuminteraction gate implemented with planar semiconductor qdots usingtunneling through oxide layer with partial overlap of semiconductor welland control gate;

FIG. 52D is a diagram illustrating an example of H-style quantuminteraction gate implemented with planar semiconductor qdots usingtunneling through local depleted region in continuous wells;

FIG. 53A is a diagram illustrating a first example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with tunnelingthrough separate layer and interaction from enlarged well islandsallowing smaller spacing and stronger interaction;

FIG. 53B is a diagram illustrating a second example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with tunnelingthrough separate layer and interaction from enlarged well islandsallowing smaller spacing and stronger interaction;

FIG. 53C is a diagram illustrating a third example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with interactionfrom enlarged well islands allowing smaller spacing and strongerinteraction;

FIG. 53D is a diagram illustrating a fourth example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with fin to fininteraction mandating larger spacing and weaker interaction;

FIG. 54 is a diagram illustrating example operation of a quantumannealing interaction gate structure;

FIG. 55 is a diagram illustrating example operation of a controlled SWAPquantum interaction gate structure;

FIG. 56 is a diagram illustrating example operation of a controlledPauli quantum interaction gate structure;

FIG. 57 is a diagram illustrating example operation of an ancillaryquantum interaction gate structure;

FIG. 58 is a high level block diagram illustrating the quantumprocessing unit (QPU) of FIG. 1 in more detail;

FIG. 59 is a diagram illustrating an example double V quantum structurewith reset, injector, imposer, and detector circuits;

FIG. 60 is a diagram illustrating an example quantum core circuit withrelated DACs and pattern generator circuits;

FIG. 61 is a diagram illustrating an example dummy referenced quantumdifferential detector;

FIG. 62 is a diagram illustrating an example self-referenced quantumdifferential detector;

FIG. 63 is a diagram illustrating an example quantum circuit withdetectors at both its complementary outputs;

FIG. 64 is a diagram illustrating an example device exclusion zonebetween the quantum core and detectors;

FIG. 65 is a diagram illustrating an example detector circuit in moredetail;

FIG. 66 is a diagram illustrating the preamp circuit portion of thedetector in more detail;

FIG. 67 is a diagram illustrating the correlated double sampler (CDS)circuit in more detail;

FIG. 68 is a diagram illustrating an example single ended CDS circuit;

FIG. 69 is a diagram illustrating an example differential CDS circuit;

FIG. 70 is a diagram illustrating an example merged semiconductorstructure and sensor using a shared well;

FIG. 71 is a diagram illustrating an example timing diagram of severalcontrols of the quantum core and detector circuits;

FIG. 72 is a diagram illustrating an example semiconductor layout of adouble V quantum structure and associated sensor devices; and

FIG. 73 is a diagram illustrating an example semiconductor layout of thequantum core and associated detector circuits.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention. Itwill be understood by those skilled in the art, however, that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Among those benefits and improvements that have been disclosed, otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingfigures. Detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the invention that may be embodied in variousforms. In addition, each of the examples given in connection with thevarious embodiments of the invention which are intended to beillustrative, and not restrictive.

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings.

The figures constitute a part of this specification and includeillustrative embodiments of the present invention and illustrate variousobjects and features thereof. Further, the figures are not necessarilyto scale, some features may be exaggerated to show details of particularcomponents. In addition, any measurements, specifications and the likeshown in the figures are intended to be illustrative, and notrestrictive. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. Further, where considered appropriate,reference numerals may be repeated among the figures to indicatecorresponding or analogous elements.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary, for the understanding andappreciation of the underlying concepts of the present invention and inorder not to obfuscate or distract from the teachings of the presentinvention.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method. Any reference inthe specification to a system should be applied mutatis mutandis to amethod that may be executed by the system.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The phrases “in one embodiment,” “in an exampleembodiment,” and “in some embodiments” as used herein do not necessarilyrefer to the same embodiment(s), though it may. Furthermore, the phrases“in another embodiment,” “in an alternative embodiment,” and “in someother embodiments” as used herein do not necessarily refer to adifferent embodiment, although it may. Thus, as described below, variousembodiments of the invention may be readily combined, without departingfrom the scope or spirit of the invention.

In addition, as used herein, the term “or” is an inclusive “or”operator, and is equivalent to the term “and/or,” unless the contextclearly dictates otherwise. The term “based on” is not exclusive andallows for being based on additional factors not described, unless thecontext clearly dictates otherwise. In addition, throughout thespecification, the meaning of “a,” “an,” and “the” include pluralreferences. The meaning of “in” includes “in” and “on.”

The following definitions apply throughout this document.

A quantum particle is defined as any atomic or subatomic particlesuitable for use in achieving the controllable quantum effect. Examplesinclude electrons, holes, ions, photons, atoms, molecules, artificialatoms. A carrier is defined as an electron or a hole in the case ofsemiconductor electrostatic qubit. Note that a particle (actually itswavefunction) may be split and present in multiple quantum dots. Thus, areference to a particle also includes split particles.

In quantum computing, the qubit is the basic unit of quantuminformation, i.e. the quantum version of the classical binary bitphysically realized with a two-state device. A qubit is a two base statequantum mechanical system in which the states can be in a superposition.Examples include (1) the spin of the particle (e.g., electron, hole) inwhich the two levels can be taken as spin up and spin down; (2) thepolarization of a single photon in which the two states can be taken tobe the vertical polarization and the horizontal polarization; and (3)the position of the particle (e.g., electron) in a structure of twoqdots, in which the two states correspond to the particle being in oneqdot or the other. In a classical system, a bit is in either one stateor the other. Quantum mechanics, however, allows the qubit to be in acoherent superposition of both states simultaneously, a propertyfundamental to quantum mechanics and quantum computing. Multiple qubitscan be further entangled with each other.

A quantum dot or qdot (also referred to in literature as QD) is ananometer-scale structure where the addition or removal of a particlechanges its properties is some ways. In one embodiment, quantum dots areconstructed in silicon semiconductor material having typical dimensionin nanometers. The position of a particle in a qdot can attain severalstates. Qdots are used to form qubits and qudits where multiple qubitsor qudits are used as a basis to implement quantum processors andcomputers.

A quantum interaction gate is defined as a basic quantum logic circuitoperating on a small number of qubits or qudits. They are the buildingblocks of quantum circuits, just like the classical logic gates are forconventional digital circuits.

A qubit or quantum bit is defined as a two state (two level) quantumstructure and is the basic unit of quantum information. A qudit isdefined as a d-state (d-level) quantum structure. A qubyte is acollection of eight qubits.

The terms control gate and control terminal are intended to refer to thesemiconductor structure fabricated over a continuous well with a localdepleted region and which divides the well into two or more qdots. Theseterms are not to be confused with quantum gates or classical fieldeffect transistor (FET) gates.

Unlike most classical logic gates, quantum logic gates are reversible.It is possible, however, although cumbersome in practice, to performclassical computing using only reversible gates. For example, thereversible Toffoli gate can implement all Boolean functions, often atthe cost of having to use ancillary bits. The Toffoli gate has a directquantum equivalent, demonstrating that quantum circuits can perform alloperations performed by classical circuits.

A quantum well is defined as a low doped or undoped continuous depletedsemiconductor well that functions to contain quantum particles in aqubit or qudit. The quantum well may or may not have contacts and metalon top. A quantum well holds one free carrier at a time or at most a fewcarriers that can exhibit single carrier behavior.

A classic well is a medium or high doped semiconductor well contactedwith metal layers to other devices and usually has a large number offree carriers that behave in a collective way, sometimes denoted as a“sea of electrons.”

A quantum structure or circuit is a plurality of quantum interactiongates. A quantum computing core is a plurality of quantum structures. Aquantum computer is a circuit having one or more computing cores. Aquantum fabric is a collection of quantum structures, circuits, orinteraction gates arranged in a grid like matrix where any desiredsignal path can be configured by appropriate configuration of accesscontrol gates placed in access paths between qdots and structures thatmake up the fabric.

In one embodiment, qdots are fabricated in low doped or undopedcontinuous depleted semiconductor wells. Note that the term ‘continuous’as used herein is intended to mean a single fabricated well (even thoughthere could be structures on top of them, such as gates, that modulatethe local well's behavior) as well as a plurality of abutting contiguouswells fabricated separately or together, and in some cases mightapparently look as somewhat discontinuous when ‘drawn’ using a computeraided design (CAD) layout tool.

The term classic or conventional circuitry (as opposed to quantumstructures or circuits) is intended to denote conventional semiconductorcircuitry used to fabricate transistors (e.g., FET, CMOS, BJT, FinFET,etc.) and integrated circuits using processes well-known in the art.

The term Rabi oscillation is intended to denote the cyclic behavior of aquantum system either with or without the presence of an oscillatorydriving field. The cyclic behavior of a quantum system without thepresence of an oscillatory driving field is also referred to asoccupancy oscillation.

Throughout this document, a representation of the state of the quantumsystem in spherical coordinates includes two angles θ and φ. Consideringa unitary sphere, as the Hilbert space is a unitary state, the state ofthe system is completely described by the vector W. The vector Ψ inspherical coordinates can be described in two angles θ and φ. The angleθ is between the vector W and the z-axis and the angle φ₂ is the anglebetween the projection of the vector on the XY plane and the x-axis.Thus, any position on the sphere is described by these two angles θ andφ. Note that for one qubit angle θ representation is in threedimensions. For multiple qubits θ representation is in higher orderdimensions.

Semiconductor Processing

Regarding semiconductor processing, numerous types of semiconductormaterial exist such as (1) single main atom types, e.g., Silicon (Si),Germanium (Ge), etc., and (2) compound material types, e.g.,Silicon-Germanium (SiGe), Indium-Phosphide (InP), Gallium-Arsenide(GaAs), etc.

A semiconductor layer is called intrinsic or undoped if no additionaldopant atoms are added to the base semiconductor crystal network. Adoped semiconductor layer is doped if other atoms (i.e. dopants) areadded to the base semiconductor crystal. The type of layer depends onthe concentration of dopant atoms that are added: (1) very low dopedsemiconductor layers having high resistivity, i.e. n−type denoted by n−−and p−type denoted by p−−, having resistivities above 100 Ohm·cm; (2)low doped semiconductor layers, i.e. p−type denoted with p− and n−typedenoted with n−, having resistivities around 10 Ohm·cm; (3) medium dopedlayers, i.e. p for p−type and n for n−type; (4) high doped layers, i.e.p+ and n+; and (5) very highly doped layers, i.e. p++ and n++.

Note that introducing dopants in a semiconductor crystal likely resultsin defects that introduce energy traps that capture mobile carriers.Traps are detrimental for semiconductor quantum structures because theycapture and interact with the quantum particles resulting in decoherenceof the quantum information. For realizing semiconductor quantumstructures undoped semiconductor layers are preferred.

Classic electronic devices use mostly low, medium, high and very highlydoped semiconductor layers. Some layers are ultra-highly doped to behaveas metals, such as the gate layer.

Semiconductor processing is typically performed on large semiconductorwafers which have a given thickness for mechanical stability. Circuitryis fabricated on a very thin layer on the top of the wafer where theunused thick portion of the wafer is termed the substrate. In a bulkprocess, devices are fabricated directly in the semiconductor body ofthe wafer.

An insulating layer (e.g., oxide) isolates from the substrate thedevices used to create circuitry. Semiconductor on insulator process,e.g., silicon on insulator (SOI), uses a layer of insulator (e.g.,oxide) between the thin top semiconductor layer where devices arerealized and the substrate.

To improve circuit performance, the wafer is processed such that thedevices are realized on top of an insulator substrate, e.g.,semiconductor-on-glass, semiconductor-on-organic material,semiconductor-on-sapphire, etc.

Alternatively, the semiconductor substrate is eliminated and replacedwith a nonelectrical conducting material such as a polymer or othermaterial compatible with a semiconductor process (e.g.,substrate-replacement processes). Substrate replacement in realizingsemiconductor quantum structures significantly reduces or eliminatessubstrate decoherence.

High resistivity (i.e. very low doped) substrates are the next bestsubstrate choice for semiconductor quantum structures. Althoughintrinsic substrates are also suitable for semiconductor quantumstructures, there are specific limitations that prevent the use ofintrinsic substrates.

Thus, in accordance with the invention, semiconductor quantum structurescan be realized in (1) bulk processes, (2) SOI processes, (3) substratereplacement processes, or (4) semiconductor on other materials.

Regarding processing, (1) planar processes may be used where layers havepredominantly one orientation, i.e. horizontal; and (2)three-dimensional processes (3D) allow layers with both horizontal andvertical orientation, realizing more complex 3D structures. It isappreciated that although layers are shown in the figures as rectangularprisms for simplicity, physically the layers have more complicatedstructures. For example, corners are often rounded and distortions arepresent due to the masking process. In depth dimension, layers tend tohave a trapezoidal shape instead of the ideal rectangular one. Thesemiconductor quantum structures of the present invention can berealized in either planar or 3D processes.

Quantum Computing System

A high-level block diagram illustrating a first example quantum computersystem constructed in accordance with the present invention is shown inFIG. 1. The quantum computer, generally referenced 10, comprises aconventional (i.e. not a quantum circuit) external support unit 12,software unit 20, cryostat unit 36, quantum processing unit 38, clockgeneration units 33, 35, and one or more communication busses betweenthe blocks. The external support unit 12 comprises operating system (OS)18 coupled to communication network 76 such as LAN, WAN, PAN, etc.,decision logic 16, and calibration block 14. Software unit 20 comprisescontrol block 22 and digital signal processor (DSP) 24 blocks incommunication with the OS 18, calibration engine/data block 26, andapplication programming interface (API) 28.

Quantum processing unit 38 comprises a plurality of quantum corecircuits 60, high speed interface 58, detectors/samplers/output buffers62, quantum error correction (QEC) 64, digital block 66, analog block68, correlated data sampler (CDS) 70 coupled to one or more analog todigital converters (ADCs) 74 as well as one or more digital to analogconverters (DACs, not shown), clock/divider/pulse generator circuit 42coupled to the output of clock generator 35 which comprises highfrequency (HF) generator 34. The quantum processing unit 38 furthercomprises serial peripheral interface (SPI) low speed interface 44,cryostat software block 46, microcode 48, command decoder 50, softwarestack 52, memory 54, and pattern generator 56. The clock generator 33comprises low frequency (LF) generator 30 and power amplifier (PA) 32,the output of which is input to the quantum processing unit (QPU) 38.Clock generator 33 also functions to aid in controlling the spin of thequantum particles in the quantum cores 60.

The cryostat unit 36 is the mechanical system that cools the QPU down tocryogenic temperatures. Typically, it is made from metal and it can befashioned to function as a cavity resonator 72. It is controlled bycooling unit control 40 via the external support unit 12. The coolingunit control 40 functions to set and regulate the temperature of thecryostat unit 36. By configuring the metal cavity appropriately, it ismade to resonate at a desired frequency. A clock is then driven via apower amplifier which is used to drive the resonator which creates amagnetic field. This magnetic field can function as an auxiliarymagnetic field to aid in controlling one or more quantum structures inthe quantum core.

The external support unit/software units may comprise any suitablecomputing device or platform such as an FPGA/SoC board. In oneembodiment, it comprises one or more general purpose CPU cores andoptionally one or more special purpose cores (e.g., DSP core, floatingpoint, etc.) that that interact with the software stack that drives thehardware, i.e. the QPU. The one or more general purpose cores executegeneral purpose opcodes while the special purpose cores executefunctions specific to their purpose. Main memory comprises dynamicrandom access memory (DRAM) or extended data out (EDO) memory, or othertypes of memory such as ROM, static RAM, flash, and non-volatile staticrandom access memory (NVSRAM), bubble memory, etc. The OS may compriseany suitable OS capable of running on the external support unit andsoftware units, e.g., Windows, MacOS, Linux, QNX, NetBSD, etc. Thesoftware stack includes the API, the calibration and management of thedata, and all the necessary controls to operate the external supportunit itself.

The clock generated by the high frequency clock generator 35 is input tothe clock divider 42 that functions to generate the signals that drivethe QPU. Low frequency clock signals are also input to and used by theQPU. A slow serial/parallel interface (SPI) 44 functions to handle thecontrol signals to configure the quantum operation in the QPU. The highspeed interface 58 is used to pump data from the classic computer, i.e.the external support unit, to the QPU. The data that the QPU operates onis provided by the external support unit.

Non-volatile memory may include various removable/non-removable,volatile/nonvolatile computer storage media, such as hard disk drivesthat reads from or writes to non-removable, nonvolatile magnetic media,a magnetic disk drive that reads from or writes to a removable,nonvolatile magnetic disk, an optical disk drive that reads from orwrites to a removable, nonvolatile optical disk such as a CD ROM orother optical media. Other removable/non-removable, volatile/nonvolatilecomputer storage media that can be used in the exemplary operatingenvironment include, but are not limited to, magnetic tape cassettes,flash memory cards, digital versatile disks, digital video tape, solidstate RAM, solid state ROM, and the like.

The computer may operate in a networked environment via connections toone or more remote computers. The remote computer may comprise apersonal computer (PC), server, router, network PC, peer device or othercommon network node, or another quantum computer, and typically includesmany or all of the elements described supra. Such networkingenvironments are commonplace in offices, enterprise-wide computernetworks, intranets and the Internet.

When used in a LAN networking environment, the computer is connected tothe LAN via network interface 76. When used in a WAN networkingenvironment, the computer includes a modem or other means forestablishing communications over the WAN, such as the Internet. Themodem, which may be internal or external, is connected to the system busvia user input interface, or other appropriate mechanism.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++, C# or the like, conventional proceduralprogramming languages, such as the “C” programming language, andfunctional programming languages such as Python, Hotlab, Prolog andLisp, machine code, assembler or any other suitable programminglanguages.

Also shown in FIG. 1 is the optional data feedback loop between thequantum processing unit 38 and the external support unit 12 provided bythe partial quantum data read out. The quantum state is stored in thequbits of the one or more quantum cores 60. The detectors 62 function tomeasure/collapse/detect some of the qubits and provide a measured signalthrough appropriate buffering to the output ADC block 74. The resultingdigitized signal is sent to the decision logic block 16 of the externalsupport unit 12 which functions to reinject the read out data back intothe quantum state through the high speed interface 58 and quantuminitialization circuits. In an alternative embodiment, the output of theADC is fed back to the input of the QPU.

In one embodiment, quantum error correction (QEC) is performed via QECblock 64 to ensure no errors corrupt the read out data that isreinjected into the overall quantum state. Errors may occur in quantumcircuits due to noise or inaccuracies similarly to classic circuits.Periodic partial reading of the quantum state function to refresh allthe qubits in time such that they maintain their accuracy for relativelylong time intervals and allow the complex computations required by aquantum computing machine.

It is appreciated that the architecture disclosed herein can beimplemented in numerous types of quantum computing machines. Examplesinclude semiconductor quantum computers, superconducting quantumcomputers, magnetic resonance quantum computers, optical quantumcomputers, etc. Further, the qubits used by the quantum computers canhave any nature, including charge qubits, spin qubits, hybridspin-charge qubits, etc.

In one embodiment, the quantum structure disclosed herein is operativeto process a single particle at a time. In this case, the particle canbe in a state of quantum superposition, i.e. distributed between two ormore locations or charge qdots. In an alternative embodiment, thequantum structure processes two or more particles at the same time thathave related spins. In such a structure, the entanglement between two ormore particles could be realized. Complex quantum computations can berealized with such a quantum interaction gate/structure or circuit.

In alternative embodiments, the quantum structure processes (1) two ormore particles at the same time having opposite spin, or (2) two or moreparticles having opposite spins but in different or alternate operationcycles at different times. In the latter embodiment, detection isperformed for each spin type separately.

A high level block diagram illustrating a generalized quantum structureinterfaced to classical integrated electronic control circuitry is shownin FIG. 2. The example quantum circuit, generally referenced 80,comprises quantum structure 84 at its core, and support circuitry thatin one embodiment is integrated on the same physical realized support orexternal on a different physical realized support. The support circuitrycomprises reset circuits 82 for flushing the quantum structure of anyavailable free carriers before starting the quantum operation and toprepare it for a new quantum operation, injector circuits 88 thatfunction to inject one or more particles into the quantum corestructure, imposer circuits 90 that control the quantum operation andthe flow of the quantum computation between the injected particles,detector circuits 86 that sense whether a particle is present or not inthe output qdots and the particles at the output points of the quantumstructure after the quantum operation has been performed, and controlcircuitry 92. Note that in one embodiment, multiple such quantumstructures/quantum cores can be interconnected and/or operated inparallel. Further note that the common electrical node of the resetcircuit 82 output and the injector circuit 88 output can be the same asthe electrical node of the detector circuit (86) input. In this case,the three circuits time-share their active operations.

To achieve quantum operation, physical structures must be cooled tocryogenic temperatures and be isolated as much as possible fromenvironmental perturbations (e.g., external electric fields and/ormagnetic fields, etc.). To perform quantum computing using particles ina semiconductor structure, the particles (e.g., electrons, holes, etc.)need to be able to be excited in quantum states and to stay in suchstates for a long enough time for the operation and measurement of thequantum operation to be realized. At higher temperatures, the thermalenergy of the particle results in the decoherence of its quantum state.

In one embodiment, the semiconductor based quantum structure uses acontinuous well with an imposing gate that generates a controlled localdepletion region to separate two or more regions of the well that formquantum dots (qdots). By modulating the potential of the imposer gate,controlled tunneling through the local depleted region is enabledbetween the plurality of sections of the continuous well, realizing thefunction of a position/charge qubit. It is appreciated that more complexstructures having a higher number of qdots per continuous well and alarger number of wells can be built using the techniques of the presentinvention. Both planar and 3D semiconductor processes can be used tobuild such well-to-well tunneling quantum structures. By combining anumber of such elementary quantum structures/gates, a quantum computingmachine is realized.

Quantum Operation

To aid in understanding the principles of the present invention, a briefexplanation of quantum operation is presented below.

As stated supra, in classic electronics, the unit of information is abit that can represent only one of the two states “0” and “1” at a giventime. Computations in classical computers are performed sequentially andevery bit can hold only one state at a time.

As stated supra, quantum electronics uses the quantum behavior ofparticles to perform computations. The unit of quantum information is aquantum bit or qubit. A qubit has two or more base states denoted by{circumflex over (0)} and {circumflex over (1)} (or |0> and |1>) but incontrast with a classic bit, a qubit can be in a superposed state thatcontains some percentage ‘a’ of state {circumflex over (0)}, and somepercentage ‘b’ of state {circumflex over (1)}, denoted by a{circumflexover (0)}+b{circumflex over (1)}. Since a qubit in quantum structurescan simultaneously be in multiple superposed states, multiple sets ofcomputations can be performed concurrently, resulting in large quantumcomputation speed-ups, when compared with classic computations.

A quantum particle is described by its position and/or spin. Theparticles used in quantum structures are called quantum particles. Thereare qubits based on the quantum position of the particles, also namedcharge-qubits, while other qubits use the spin of the quantum particles,also named spin-qubits. In quantum structures, the charge carriers areheld in specific regions called quantum dots or qdots. A quantumstructure is constructed from one or more qdots.

Performing a quantum computation involves several steps. First thestructure needs to be reset, which means that all the free carriers(e.g., electrons or holes) from the structure need to be flushed out.Once the free carriers are removed, the structure is initialized meaningparticles are introduced in one of the base states (e.g., {circumflexover (0)} or {circumflex over (1)}). In the case of a charge-qubit(position-qubit) it means that a carrier is loaded in one of the qdots.A free carrier not coming from the quantum initialization process caninteract with the quantum particles and result in decoherence, i.e. lossof quantum information. After the particles have been loaded in thecorresponding base states they undergo the desired quantum operationunder control of gate control terminals. Once the desired quantumoperations are complete a detection is performed whereby the presence orabsence of a particle in a given qdot at a given time is tested.Detection is usually destructive which means that the quantum particle'swavefunction and its state collapse. Special nondestructivedetection/measurement exist that do not collapse the quantum state. Insuch cases, multiple measurements of the same quantum state can beperformed.

The position of a quantum particle is given by the region where theparticle wave-function is mostly present. In one embodiment, quantumstructures use semiconductor qdots realized with semiconductor wellswhere the particle transport is done through tunneling which is aquantum effect. The tunneling or particle transport is controlled bycontrol terminals. In one embodiment, the control terminals are realizedusing gates but they may comprise other semiconductor process layers.

To illustrate, consider a generic position double qdot structure havinga “dog bone” shape shown in FIG. 3A. The structure comprises a controlgate 974 giving rise to two qdots 970, 972, that correspond to the |0>and |1> base states, or “left” and “right” base states, when anelectrostatic particle happens to be there. Higher order positionquantum structures can be realized having more than two base states andthus use more than two qdots. The particle transport from one qdot tothe other is done through tunneling. Before initialization both qdotsmust be cleared of quantum particles since a reset flushes out all freecarriers.

Note that a key difference between the classic and quantumstructures/circuits is that the structure can not only be in the basestates |0> and |1>, but also in a superposed position a|0>+b|1>, with aconstraint |a|²+|b|²=1, meaning the particle is present simultaneouslyin both qdots of the structure. When the signal on the control terminalcauses a lowering of the tunneling barrier, the particle initiallyloaded in the left qdot 970 will tunnel to the right qdot 972. Theposition of the particle and thus the corresponding quantum state isgiven by the pulse width of the signal V_(control) applied to thecontrol gate. If the pulse width is long enough, after the particle hastunneled to the right qdot 972 it will tunnel back to the left qdot 970and then again to the right qdot 972 and the process repeats itself inan oscillatory fashion. The period of this oscillation, called the Rabioscillation (especially in case of a time-dependent Hamiltonian),depends on the tunnel current and thus on the control signal V_(control)applied and the configuration and process of the specific structure. Thetime needed for a particle to tunnel forward and then back to itsinitial position is called the Rabi period.

The Rabi oscillation after reset but before initialization is shown inFIG. 3B where waveform 976 represents an ideal oscillation and waveform978 represents oscillation with some amount of decoherence or leakage ofwavefunction.

Consider a quantum particle 976 loaded in the left qdot 970 with a basestate |0>, as shown in FIG. 3C. The Rabi oscillation waveform atinitialization (dot referenced 980) is shown in FIG. 3D. In ahorizontally oriented double qdot, a quantum particle 976 loaded in theright qdot 972 is considered in the base state |1>, as shown in FIG. 3E.Similarly, the up and down qdots correspond to the |0> and |1> basestates in a vertically oriented double qdot. The control terminal(typically the gate) determines the height of the tunnel barrier. If thepotential barrier is high then tunneling is blocked (i.e. negligible).On the other hand, if the potential barrier is low then tunneling isallowed and the particle moves from one qdot to the other, resulting ina change in quantum state.

If the control signal pulse width is equal to half the Rabi period asshown in FIG. 3F, then the particle will tunnel from the left qdot 970to the right qdot 972, i.e. transition from the |0> base state to the|1> base state also known as a quantum inversion, trajectory of which isrepresented by waveform solid portion 982.

If the control pulse width is equal to one quarter of the Rabi period asrepresented by waveform solid portion 984 trajectory in FIG. 3H, thenthe particle will be present equally in the left qdot 970 and in theright qdot 972 as shown in FIG. 3G. This equal distribution quantumstate is called the Hadamard state and is fundamental for quantumcomputation. The double qdot with a quarter Rabi period control signalperforms the function of a fundamental Hadamard quantum gate.Considering the sinewave of an oscillatory effect, the Hadamard statecorresponds to the zero crossings, while the peak of the positive cyclecorresponds to the base state |0> and the peak of the negative cyclecorresponds to the base state |1>. All points between the positive andnegative peaks correspond to superposition states.

If the pulse width of the control signal is less than one quarter theRabi period as represented by solid waveform portion 986 in FIG. 3J,then the quantum particle is split between the two qdots as shown inFIG. 3I but it will have a larger presence in the left qdot 970 versusthe right qdot 972. Similarly, if the pulse width is larger than onequarter the Rabi period as represented by solid waveform portion 988 inFIG. 3L, than the quantum particle is split as shown in FIG. 3K but willhave a larger presence in the right qdot 972.

If the position of the particle is represented as a vector of constantlength in a circular coordinate system, a vector pointing up representsthe |0> base state, while a vector pointing down represents the |1> basestate. Any other position is a superposed state that constitutes aquantum rotation operation. As such the double qdot quantum structurewith a variable control signal pulse width constitutes a controlledquantum rotation gate.

The initialization of a quantum structure is realized by an interfacedevice (described in more detail infra) having one side connected toclassical circuitry and the other side connected to quantum circuitry,i.e. half classic, half quantum. On the classic side, the carriers(e.g., electrons or holes) have a collective behavior, sometimes calleda sea of electrons (or holes). On the quantum side, the carriers exhibitsingle charge carrier or a few carrier behavior and their interaction isbased on the laws of quantum mechanics. Injecting exactly a singleparticle in the quantum structure at a given qdot can be realizedthrough the tunneling effect in the interface device. Once a singleparticle has tunneled, the electric field changes such that it opposesthe tunneling of a subsequent particle. Such behavior of the interfacedevice is critical to be able to inject one or multiple single particlesinto one or multiple qdots of a given quantum structure.

The pulse width of the control signals can be digitally controlled onthe classical side of the circuits and thus determine what kind ofquantum operation is performed, resulting in a programmable quantummachine. In this case, the same hardware implementation is able toperform different quantum operations based on the specific controlsignal applied.

Note that each quantum particle injected into the quantum structurerepresents a qubit. In the position qubit at least two qdots are neededto implement a qubit. In the general case, structures with N qubits andM qdots can be constructed. The number of injectors, however, should beequal to N if all particles are injected at the same time, or it can belower than N if the particles are injected at different times.

A diagram illustrating a circular shaped semiconductor quantum structureincorporating local depleted well tunneling is shown in FIG. 4A. Thequantum structure, generally referenced 100, comprises a continuous wellwith a local depleted region with a control gate 106 fabricated over itthat functions to separate the well into two or more portions eachimplementing a qdot. In this example, the continuous well is split intotwo qdots 102, 104 with a tunneling path 108 formed between them for thequantum particle 110, e.g., electron, to tunnel through. The tunnelingpath 108 is considered to effectively connect the two wells 102 and 104in a quantum manner. The quantum operation is controlled by the gate 106fabricated over the tunneling path 108. The gate functions to modulatethe energy barrier created by the local depleted region. The twosections of the well, the tunneling path with the local depleted region,and the control gate can take any number of different shapes (describedinfra) allowed by the particular semiconductor process used (planar or3D).

In one embodiment, the two qdots 102, 104 are linked by a region 108that is partially or completely locally depleted and in which tunnelingoccurs as indicated by arrow 109 through the tunneling path. The controlgate typically overlaps the tunneling path in order to maintainwell-controlled depletion of the entire linking region between the twoqdots. This prevents direct electric conduction between the two qdots.

The depletion region is required for quantum operation of the structure.If there were no depletion region, the operation would revert to aclassical transistor operation in on/off modes and the particle cannormally move from one side to the other. Note that the probability of aparticle tunneling through the depletion region is approximatelyexponentially linked to the width of the depletion region. If thedepletion region is very narrow, the particle will tunnel and thequantum operation is achieved. If the depletion region is wide, thenthere is no tunneling or the tunneling is so weak that it can beneglected. This is also dependent on the tunneling barrier height. For ap−type semiconductor material, placing a positive potential on the gatewill repel the holes and create a depletion region. Note that thevoltage is necessarily lower than the level that results in the creationof an inversion channel.

The control signals that need to be applied to the gate depend onwhether the semiconductor material is p or n type. Consider for examplep−type semiconductor material, with no potential on the gate, theparticle may be free to tunnel. Placing a positive potential on the gatewill repel the particles (i.e. holes) and create the depletion regionthereby hindering tunneling. If the potential on the gate is removed orbrought closer to zero to zero or made negative, the particles arepermitted to tunnel in relation to the potential applied. The operationof the quantum structure is significantly different than that of aconventional transistor.

In one embodiment, the two qdots 102, 104 are realized by a singlesemiconductor well having a polysilicon gate on top. The tunnelinghappens laterally or horizontally through the depleted region thatisolates the two qdots.

Note also that in one embodiment the well is surrounded by oxide,isolating layers, and/or one or more wide depletion regions that preventthe quantum particle from escaping from the well.

A diagram illustrating the change in the aperture tunnel barrier from awide depletion region to a narrow depletion region is shown in FIG. 4B.To contain or trap the quantum particle 114, the barrier potential 112between the two wells is made high (dashed line 116). Lowering thebarrier potential between the two wells (solid line below the dashedline) enables the quantum particle to tunnel from one qdot to the other.

A diagram illustrating a first rectangular shaped semiconductor quantumstructure incorporating local depleted well tunneling is shown in FIG.4C. The quantum structure, generally referenced 120, is similar tostructure 100 of FIG. 4A apart from the dog bone shape of the continuouslocal depleted well. Control gate 126 is fabricated over the well andfunctions to separate the well into two qdots 122, 124 with tunnelingpath 128 formed between them for the quantum particle 130 to tunnelthrough. The quantum operation is controlled by the gate 126 fabricatedover the tunneling path 128. The gate functions to modulate the barriercreated by the local depleted region.

The two qdots 122, 124 are linked by a region 128 that is partially orcompletely locally depleted and in which tunneling occurs as indicatedby arrow 129 through the tunneling path. The control gate typicallyoverlaps the tunneling path in order to maintain well-controlleddepletion of the entire linking region between the two Qdots. Thisprevents direct electric conduction between the two qdots.

A diagram illustrating the change in the aperture tunnel barrier from awide depletion region to a narrow depletion region is shown in FIG. 4D.To contain or trap the quantum particle 134, the barrier potential 132between the two wells is made high (dashed line 136). Lowering thebarrier potential (solid line) enables the quantum particle to tunnelfrom one qdot to the other.

A diagram illustrating a second rectangular shaped semiconductor quantumstructure incorporating local depleted well tunneling is shown in FIG.5. The quantum structure, generally referenced 140, is similar tostructure 100 of FIG. 4A apart from the ‘S’ shape of the continuous wellwith local depleted region. Control gate 146 is fabricated over the welland functions to separate the well into two qdots 142, 144 withtunneling path 148 formed between them for the quantum particle 149 totunnel through. The quantum operation is controlled by the gate 146fabricated over the tunneling path 148. The gate functions to modulatethe barrier created by the local depleted region.

The two qdots 142, 144 are linked by a region 148 that is partially orcompletely locally depleted and in which tunneling occurs as indicatedby arrow 147 through the tunneling path. The control gate typicallyoverlaps the tunneling path in order to maintain well-controlleddepletion of the entire linking region between the two Qdots. Thisprevents direct electric conduction between the two qdots.

A diagram illustrating a cross section of an example semiconductorquantum structure 150 is shown in FIG. 6. An exemplary cross section ina silicon-on-insulator (SOI) process is shown in which the substrate 152is low doped (i.e. high resistivity) and is isolated from the quantumdevice with a buried oxide layer (BOX) 154. This reduces the decoherenceof the quantum particle. In one embodiment, the semiconductor quantumdevice employs tunneling through the local depleted region. In anotherembodiment, tunneling occurs through the oxide layer between thesemiconductor well 160 (low doped or undoped) and the partiallyoverlapping gate 158 and oxide layer 166. The active layer 160 isisolated using oxide from adjacent structures, e.g., shallow trenchisolation (STI) 156, reducing further the quantum particle decoherence.

Note that the substrate may comprise (1) a semiconductor, (2) silicon oninsulator (SOI) substrate, where the substrate comprises sapphire,glass, organic material, etc., (3) an insulating substrate replacement,for example, sapphire, glass, organic material, plastic, polymer, etc.,or (4) any other insulating material compatible with a semiconductorprocess.

Note that regardless of the substrate used, the quantum structure mustbe electrically isolated from the substrate for the structure to operateproperly. Otherwise, the quantum particle may escape thus preventingquantum operation of the structure.

Several ways to electrically isolate the quantum structure include: (1)utilizing an SOI or low doped substrate where the oxide layerelectrically isolates the quantum structure from the substrate; (2)using substrate replacement such as an insulator material, e.g.,polymer, glass, etc.; and (3) using a fixed depletion region, as thequantum particle can tunnel only through a relatively narrow insulatingregion such as very thin oxide or a thin depletion region. If thedepletion region is too wide, the quantum particle is prevented fromtraveling. Note that this last option can be fabricated using bulkprocesses.

The quantum operation is controlled by the gate located over thetunneling path that modulates the barrier created by the local depletionregion.

In one embodiment, a low doped substrate interacts with the quantumparticle with far and weak interactions. Tunneling of the quantumparticle 162 occurs in region 164 between the two qdots formed in theactive layer 160 and the tunnel path may be straight through from oneqdot to the other (see dashed arrow 168) or may take a path through thegate and back to the active layer (see dashed arrow 169). Alternatively,the substrate may comprise a substrate replacement that includesnon-conducting material, e.g., polymer, glass, sapphire, without freecharge or ions that can interact with the quantum particle.

In both cases, the active well is preferably isolated on all sides (i.e.typically with oxide) where the particles are permitted to travel onlythrough a narrow link where tunneling occurs.

Alternatively, bulk semiconductor processes are used where the substrate152 is isolated from the quantum device using a large depleted regionunder the quantum gate instead of BOX. In another alternativeembodiment, the quantum device is placed directly into the substrate.The quantum device can be isolated laterally from other devices usingoxide layers 156 (e.g., STI or another preferably low doped well). Inanother alternative embodiment, a bulk semiconductor quantum structurereplaces the substrate with an isolator material 152 having no freecarriers or ions that can interact with the quantum particle. In analternative embodiment, a substrate replacement process or asemiconductor on insulator process can also be used.

The cross section 150 shows the quantum structure with well-to-welltunneling through the local depleted region. It is noted that if thedepleted region 164 is wide, then no or negligible tunneling 168 ispresent. If under the control of the gate the tunneling barrier islowered and the depletion region gets narrower, a sizeable tunnelingcurrent may occur, resulting in the quantum particle tunneling from oneqdot to the other.

Note that tunneling is also possible from the well to the gate and thenfrom the gate to the adjacent well, bypassing the local depleted area(arrow 169). The width of the depleted area, however, can be madenarrower than the thin gate oxide and thus the predominant tunneling canbe made to be through the local depleted region.

In some cases, the gate oxide thickness is reduced using specialmaterials such as hafnium oxide. The tunneling barrier height, however,is still high and tunneling is likely to happen through the depletionlayer.

In accordance with the present invention, the quantum structure maycomprise numerous shapes and sizes constrained only by design rule check(DRC) of the particular semiconductor process used to fabricate thestructure. Several examples of quantum structure shapes, e.g., circles,squares, rectangles, polygons, etc. will now be described. In each case,these shapes can be used for the constituent layers and for one or moreqdots making up the quantum structure.

A double qdot quantum structure which is the elementary structure forposition qubit quantum computing contains two quantum dots and atunneling path (often narrow) between them.

Quantum Structure Shapes

A diagram illustrating an example circular shape 170 for the quantumstructure of the present invention is shown in FIG. 7A. A diagramillustrating an example square shape 172 for the quantum structure ofthe present invention is shown in FIG. 7B. A diagram illustrating anexample square shape with rounded corners 174 for the quantum structureof the present invention is shown in FIG. 7C. A diagram illustrating anexample hexagonal shape 176 for the quantum structure of the presentinvention is shown in FIG. 7D. A diagram illustrating an examplerectangular shape 178 for the quantum structure of the present inventionis shown in FIG. 7E.

A diagram illustrating an example trapezoidal shape 180 for the quantumstructure of the present invention is shown in FIG. 7F. A diagramillustrating a first example overlapping square shape 182 for thequantum structure of the present invention is shown in FIG. 7G. Adiagram illustrating a first example ‘L’ shape 184 for the quantumstructure of the present invention is shown in FIG. 7H. A diagramillustrating an example ‘S’ shape 186 for the quantum structure of thepresent invention is shown in FIG. 7I. A diagram illustrating a secondexample ‘L’ shape 188 for the quantum structure of the present inventionis shown in FIG. 7J.

A diagram illustrating an example barely touching squares shape 189 forthe quantum structure of the present invention is shown in FIG. 7K. Notethat in this example shape and others it is preferable that the squaresoverlap as little as possible since it is desirable to have as narrow atunneling region as possible to maximize control. A large tunneling areais more difficult to control and to deplete sufficiently to preventpartial or complete tunneling.

A diagram illustrating an example barely touching square shape 190 withoptical proximity control 192 for the quantum structure of the presentinvention is shown in FIG. 7L. A diagram illustrating an example doublesquares 194 with narrow neck 196 shape for the quantum structure of thepresent invention is shown in FIG. 7M. A diagram illustrating a secondexample overlapping square shape 198 for the quantum structure of thepresent invention is shown in FIG. 7N. A diagram illustrating a thirdexample overlapping square shape 200 for the quantum structure of thepresent invention is shown in FIG. 7O.

A diagram illustrating an example barely touching rectangular shape 202for the quantum structure of the present invention is shown in FIG. 7P.A diagram illustrating an example barely touching double overlappingsquares shape 222 for the quantum structure of the present invention isshown in FIG. 7Q. A diagram illustrating an example double squaresconnected via single smaller square shape 208 for the quantum structureof the present invention is shown in FIG. 7R. A diagram illustrating anexample double squares connected via double smaller squares shape 204for the quantum structure of the present invention is shown in FIG. 7S.

Several alternative ways of imposing the potential on the control gatewill now be described. For illustration purposes only, doubleoverlapping square shapes are used for the qdots. It is appreciated thatother shapes may be used with each technique without departing from thescope of the invention. Note that the width of the tunneling section ofthe continuous well in each case is preferably as small as possible, butcan vary in size based on the given DRC of the semiconductor processused.

Control Gate

A diagram illustrating a first example control gate for the quantumstructure of the present invention is shown in FIG. 8A. The quantumstructure, generally referenced 220, comprises a floating control gate226 with an adjacent gate 222 that is in close proximity thereto thatimposes potential to the gate 226 of the double overlapping squareshaped qdots 224 with tunnel path 228. Note that changing the potentialof the overlapping control gate is operative to modulate the tunnelbarrier height.

A diagram illustrating a second example control gate for the quantumstructure of the present invention is shown in FIG. 8B. The quantumstructure, generally referenced 230, comprises a metal control gate 232imposing on the floating control gate 234 using adjacent or overlappositioning over the control gate 234 of the double overlapping squareshaped qdots 236 with tunnel path 238.

A diagram illustrating a third example control gate for the quantumstructure of the present invention is shown in FIG. 8C. The quantumstructure, generally referenced 240, comprises a contact 244 from ametal feed 242 to a control gate 246 over double overlapping squareshaped qdots 248 with tunnel path 249. The control gate is drivendirectly with an electrical signal (e.g., pulsed electric signal).

Quantum Structures with Control Gates

As described supra, the quantum structure may comprise numerous shapesand sizes constrained only by design rule check (DRC) of the particularsemiconductor process used to fabricate the structure. Several examplesof quantum structures having one or more control gates will now bedescribed. It is important to note that there is a difference betweenthe shapes drawn in the figures and the physical realized shapes.Further, several factors such as the semiconductor process usedcontribute to determining the physical shapes realized. Note also thatin most cases, the link channel is mandatory for the quantum structuresemploying tunneling through the depletion region. The link channel,however, may not be present on the layers drawn in the figures.

Each semiconductor quantum structure disclosed uses well-to-welltunneling through a local depleted region. In order to exercise goodcontrol over the tunneling effect, the tunneling path section of thewell is preferably relatively narrow when compared with the dimensionsof the rest of the well that constitutes the qdots. A gate is placed ontop of the tunneling path section of the well in which the localdepleted region is induced. A complete overlap of the control gate onthe tunneling path is preferable in order to have good control over theentire width of the tunneling path and achieve reliable isolationbetween the two or more sections of the continuous well that implementsthe quantum dots. The potential on the control gate functions tomodulate the width of the local depletion region and to control thetunneling between the two adjacent sections of the well that representtwo separate qdots (i.e. well-to-well tunneling). As described supra,this potential is imposed, for example, by another metal layer with nocontact to gate 226 (i.e. a floating gate) as shown in FIG. 8A or with ametal layer contacted to the gate (i.e. directly driven gate) as shownin FIG. 8C. The overlapping gate is positioned such that a smalleroverlap with the two adjacent sections of the well is realized resultingin a larger Coulomb blockade voltage.

A diagram illustrating an example quantum structure with double squarecorner touching shape is shown in FIG. 9A. The quantum structure,generally referenced 250, comprises a continuous well with control gate254 placed over edge portions 251, 253 of the square shapes to form twoqdot regions 252.

A diagram illustrating an example quantum structure with double squareshape and optical proximity control is shown in FIG. 9B. The quantumstructure, generally referenced 260, comprises a continuous well withcontrol gate 264 placed over edge portions of the square shapes to formtwo qdot regions 262. Optical proximity control 266 is used to improvethe tunnel path. As is known in the semiconductor processing arts,optical proximity correction can be used within the vicinity of thelocal depleted tunneling well to aid in improving the resultingstructures fabricated on the substrate. Note that optical proximitycorrection techniques may be used with any of the structures disclosedin this document to improve the resulting structures. Note that thesquares 266 shown only exist on one or more masks used in thefabrication of the structure and do not reflect any structures actuallybuilt on the substrate. These squares, however, typically have an effecton the shape of such structures constructed nearby. The desired effectsinclude width and length adjustments of the tunneling path.

Note that in general, nanometer semiconductor processes natively yielddistortions around corners and the narrow features. Optical correctionhelps realize physical shapes close to the desired shapes.

A diagram illustrating an example quantum structure with double squareand narrow neck shape is shown in FIG. 9C. The quantum structure,generally referenced 270, comprises a continuous well with control gate274 placed over narrow tunnel path 276 and edge portions of the squareshapes to form two qdot regions 272.

A diagram illustrating a first example quantum structure with doubleoverlapping square shape is shown in FIG. 9D. The quantum structure,generally referenced 280, comprises a continuous well with control gate284 placed over narrow tunnel path 286 (but wider than tunnel path 296in FIG. 9E) and edge portions of the square shapes to form two qdotregions 282.

A diagram illustrating a second example quantum structure with doubleoverlapping square shape is shown in FIG. 9E. The quantum structure,generally referenced 290, comprises a continuous well with control gate294 placed over narrow tunnel path 296 and edge portions of the squareshapes to form two qdot regions 292.

A diagram illustrating an example quantum structure with 1′ shape isshown in FIG. 9F. The quantum structure, generally referenced 300,comprises a continuous well with control gate 304 placed over thetransition portion of the rectangular shapes to form two qdot regions302.

A diagram illustrating an example quantum structure with double roundedbarely touching square shape is shown in FIG. 9G. The quantum structure,generally referenced 310, comprises a continuous well with control gate314 placed over narrow tunnel path 316 and edge portions of the roundedsquare shapes to form two qdot regions 312.

A diagram illustrating an example quantum structure with doublerectangular shape is shown in FIG. 9H. The quantum structure, generallyreferenced 320, comprises a continuous well with control gate 324 placedover narrow tunnel path 326 and edge portions of the rectangular shapesto form two qdot regions 322.

A diagram illustrating an example quantum structure with double squareconnected via double smaller square shape is shown in FIG. 9I. Opticalproximity correction is used here to turn the small feature connectingshapes into a narrow continuous link channel. The quantum structure,generally referenced 330, comprises a continuous well with control gate334 placed over double small square tunnel path 336 and edge portions ofthe square shapes to form two qdot regions 332.

A diagram illustrating an example quantum structure with double roundedsquare with narrow neck shape is shown in FIG. 9J. The quantumstructure, generally referenced 340, comprises a continuous well withcontrol gate 344 placed over contoured narrow tunnel path 346 and edgeportions of the rounded square shapes to form two qdot regions 342.

A diagram illustrating an example quantum structure with an overlappingpair of double rounded squares with narrow neck shape is shown in FIG.9K. The quantum structure, generally referenced 350, comprises acontinuous well with two control gates 354 placed over a contourednarrow tunnel path 356 and edge portions of the rounded square shapes toform three qdot regions 352. Note that the middle qdot is longer, beingcomprised of two semiconductor squares.

A diagram illustrating a first example quantum structure with a pair ofbarely touching double overlapping square shape is shown in FIG. 9L. Thequantum structure, generally referenced 360, comprises a continuous wellwith control gate 364 placed over tunnel path 366 and edge portions ofthe double square shapes to form two qdot regions 362.

A diagram illustrating a second example quantum structure with a pair ofdouble corner overlapping square shape is shown in FIG. 9M. The quantumstructure, generally referenced 370, comprises a continuous well withtwo floating control gates 374 with adjacent imposing gate potentialplaced over tunnel paths 378 and edge portions of the square shapes toform three qdot regions 372. Note that the middle qdot is formed by twosquares of active silicon.

A diagram illustrating a first example quantum structure with a doublesquare shape with narrow neck and butterfly shaped control gate is shownin FIG. 9N. Note that most of the quantum structures described supracomprise square or rectangular shaped gates. Some availablesemiconductor processes, however, allow for composed shapes for thegate. In these cases, both the well and the gate have a narrowconnecting channel. The quantum structure, generally referenced 380,comprises a continuous well with control gate 382 placed over narrowtunnel path 386 to form two qdot regions 384. Here, the gate and thewell both have narrow connecting channels. This structure results in amuch smaller gate to well overlap resulting in a much higher Coulombblockade voltage for the structure. This enables a higher performance ofthe quantum structure since a larger signal to noise ratio is achieved.

A diagram illustrating a second example quantum structure with a doublesquare shape with narrow neck and butterfly shaped control gate is shownin FIG. 9O. Similar to the structure of FIG. 9N, the quantum structure,generally referenced 390, comprises a continuous well with control gate392 placed over contoured narrow necked tunnel path 396 to form tworounded square qdot regions 392. Here too, the gate and the well bothhave narrow connecting channels.

A diagram illustrating an example quantum structure with a pair ofoverlapping double square shapes with narrow neck and butterfly shapedcontrol gates is shown in FIG. 9P. The quantum structure, generallyreferenced 400, comprises a continuous well with two floating controlgates 402 electrostatically coupled to adjacent imposing gates 406placed over contoured narrow necked tunnel paths 408 to form threerounded square qdot regions 404 with the gates 406 and the wells havingnarrow connecting channels.

A diagram illustrating an example conventional field effect transistor(FET) with drain and source doped diffusion and contacts is shown inFIG. 9Q. Using a conventional field effect transistor (FET) structure tobuild semiconductor quantum structures results in significantly degradedperformance. In one embodiment, a modified semiconductor process is usedto construct optimized semiconductor quantum structures.

Conventional wells have rectangular shapes disposed parallel to eachother. In one embodiment, the quantum structure uses (1) staircase wellshapes that provide pairs of locations where the interaction betweenquantum particles/states is very strong and (2) other pairs of locationsthat have weak or negligible interaction between the particles situatedat those locations.

The conventional FET structure, generally referenced 410, comprisesdrain and source doped diffusion with contacts 412 with metal on top,and gate 416 with contacts 414. This structure results in significantlyhigher parasitic gate capacitance since it includes the gate-to-metal,gate-to-contact and gate-to diffusion additional components. Note thatin classic FET structures, carriers move either through drift under anexternal electric field or through diffusion due to a gradient ofconcentration. An inversion channel is created by a relatively largegate voltage.

A diagram illustrating an example half conventional FET and half(potentially) quantum structure is shown in FIG. 9R. In accordance withthe present invention, a modified semiconductor process enables anactive layer without any diffusion, contact and metal on top. Thestructure, generally referenced 420, comprises a conventional doped side422 with diffusion contacts, an undoped or lightly doped quantum side426, and gate 427 with contacts 424. Such a structure has ahalf-classic, half-quantum structure with one side of the gate withoutany n or p doping and without contacts. This type of device can be used,for example, at the interface between classic circuits and quantumcircuits. In this case, the carriers move through tunneling from theclassic side to the quantum side.

A diagram illustrating an example quantum structure with rectangularshaped wells is shown in FIG. 9S. The full quantum structure, generallyreferenced 430, does not have any n or p doping or contacts on eitherside. Both sides 432 of the gate 436 with contacts 434 have the sameactive layer width which is approximately equal to the gate width. Thisresults in a larger gate capacitance. To reduce the parasitic gatecapacitance, the width of the active layer may be made smaller than thegate width on one or both sides.

A diagram illustrating an example quantum structure with dissimilarrectangular shaped wells is shown in FIG. 9T. The structure, generallyreferenced 440, comprises an asymmetric aperture tunneling well withgate 446 and gate contacts 448 placed thereover to generate two qdots442, 444 with reduced parasitic capacitance on the right side qdot.

A diagram illustrating an example quantum structure with offsetrectangular shaped wells is shown in FIG. 9U. The structure, generallyreferenced 450, comprises an asymmetric aperture tunneling well withgate 456 and gate contacts 458 placed thereover to generate two qdots452, 454 with both qdots having reduced parasitic capacitance.

Using active wells having different widths on the both sides of the gatereduces the parasitic gate capacitance. A more significant reduction ingate capacitance can be achieved, however, by having an active wellstructure having a narrow region under the gate and wider regions oneither side of the gate.

A diagram illustrating a first example quantum structure with spacedapart rectangular shaped wells is shown in FIG. 9V. The structure,generally referenced 460, comprises a symmetric dog bone aperturetunneling well with gate 466 having gate contacts 468 placed thereoverto generate two qdots 462, 464 with reduced parasitic capacitance onboth sides. Note, however, that there remains a residual overlap of thegate and the wider active wells on the two sides of the gate. Note thatthe aperture refers to the narrowed link channel between the two widerwell regions.

A diagram illustrating a first example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9W. The structure, generally referenced 470, comprises an asymmetric dogbone aperture tunneling well with gate 476 and gate contacts 478 placedthereover to generate two qdots 472, 474 with reduced parasiticcapacitance on both sides. Note, however, that there remains a residualoverlap of the gate and the wider active wells on the two sides of thegate.

In one embodiment, to further reduce gate capacitance the overlapbetween the gate and the wider wells on the sides are eliminated. Adiagram illustrating a second example quantum structure with spacedapart rectangular shaped wells is shown in FIG. 9X. The structure,generally referenced 480, comprises a symmetric dog bone aperturetunneling well with gate 486 and gate contacts 488 placed thereover togenerate two qdots 482, 484 with reduced parasitic capacitance on bothsides and no well-gate overlap in the wider regions.

A diagram illustrating a second example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9Y. The structure, generally referenced 490, comprises an asymmetric dogbone aperture tunneling well with gate 496 and gate contacts 498 placedthereover to generate two qdots 492, 494 with reduced parasiticcapacitance on both sides and no well-gate overlap in the wider regions.

As described supra, the quantum structure may be symmetric orasymmetric. The “dog-bone” quantum structure has some overhang of thewider wells passed the edge of the narrow link. The asymmetric dog bonequantum structure does not have any overhang on the narrow link side. Adiagram illustrating a third example quantum structure with spaced apartrectangular shaped wells offset from each other is shown in FIG. 9Z. Thestructure, generally referenced 500, comprises an asymmetric dog boneaperture tunneling well with partial overlap of the gate on the widewells and overhang passed the narrow link edges, and with gate 506 andgate contacts 508 placed thereover to generate two qdots 502, 504.

A diagram illustrating a fourth example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9AA. The structure, generally referenced 510, comprises an asymmetricdog bone aperture tunneling well with partial overlap of the gate on thewide wells and overhang passed the narrow link edges, and with gate 516and gate contacts 518 placed thereover to generate two qdots 512, 514with increased gate to well capacitance, but which may ease thefabrication process.

Narrow links between the two wider wells may be realized without havingthem drawn as such. In one embodiment, two wells have a punctual drawncontact but during fabrication a narrow link channel is formed betweenthe two wells using optical proximity correction. A diagram illustratinga first example quantum structure with corner abutting rectangularshaped wells is shown in FIG. 9AB. The structure, generally referenced520, comprises an aperture tunneling well with punctual drawn linkbetween the two wells, and with gate 526 and contacts 528 placedthereover to generate two qdots 522, 524.

A diagram illustrating a second example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AC. The structure,generally referenced 530, comprises the physical realization of thestructure of FIG. 9AB with a narrow link channel formed between the twowells using a suitable technique such as optical proximity correctionchannel, and with gate 536 and contacts 538 placed thereover to generatetwo qdots 532, 534.

Note that it is not mandatory that the two wide wells have a punctualcontact in order to obtain a narrow link channel between them. In somecases, it is sufficient that they are placed in very close proximity,and optical proximity correction results in a link channel in thephysically realized shapes.

A diagram illustrating a third example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AD. The structure,generally referenced 540, comprises an aperture tunneling well withoutcontact between the two wells but in very close proximity, and with gate546 and contacts 548 placed thereover to generate two qdots 542, 544.

A diagram illustrating a fourth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AE. The structure,generally referenced 550, comprises the physical realization of thestructure of FIG. 9AD with a narrow link channel formed between the twowells using a suitable technique such as optical proximity correctionchannel, and with gate 556 and contacts 558 placed thereover to generatetwo qdots 552, 554.

Note that the narrow channel link of the induced depletion regionseparating the two wider quantum wells can have any given orientation,e.g., horizontal, vertical, or any arbitrary angle. In addition, thecontrol gate may overlap the narrow channel link, or it may also overlapthe edges of the adjacent wider quantum wells. The former is preferredsince it results in a smaller parasitic capacitance and thus a largerCoulomb blockade voltage.

A diagram illustrating a fifth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AF. The structure,generally referenced 560, comprises an aperture tunneling well with anangled drawn link between the two wells and gate overlap only on thelink channel 569, and with gate 566 and gate contacts 568 placedthereover to generate two qdots 562, 564.

A diagram illustrating a sixth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AG. The structure,generally referenced 570, comprises an aperture tunneling well with anangled drawn link between the two wells and gate overlap on both thelink channel 579 and the wells themselves, and with gate 576 andcontacts 578 placed thereover to generate two qdots 572, 574.

It is appreciated that the fabrication of the quantum structure examplesdescribed supra is not limited to one process only but can be fabricatedusing any number of semiconductor processes. Examples include (1) planarsemiconductor processes with depletion tunneling, (2) planarsemiconductor processes with oxide tunneling, (3) 3D (FinFET)semiconductor processes with depletion tunneling, and (4) 3D (FinFET)semiconductor processes with oxide tunneling.

Single Particle Operation

It is important to note that to achieve quantum operation: (1) carriers(electrons or holes) need to be isolated, (2) information needs to beconveyed to the electrons in either their position or spin (or both),and (3) multiple carriers are allowed to interact (i.e. entangle) beforea reading (referred to as detection) of the quantum state is performed.

First, single carriers are separated out of the collectivities ofcarriers that usually exist in semiconductor layers in classic circuits.A semiconductor layer is formed of a network of semiconductor atoms thatcontribute carriers to a collective of carriers described by an energyband. Dopants are introduced into semiconductor layers in order toenhance the concentration of a given type of carriers. Donor dopantsincrease the number of electrons yielding an N−type semiconductor layerwhile acceptor dopants increase the number of holes yielding a P−typesemiconductor layer.

When the semiconductor contains a very large number of carriers actingas a collectivity, adding one carrier to the collectivity or subtractingone carrier from the collectivity does not change the potential. Toachieve a single carrier (e.g., single electron) behavior it is bestthat the considered particle does not have a large collectivity ofcarriers that it can interact with.

An undoped semiconductor or undoped semiconductor layer has a very lowconcentration of carriers. It still contains a large number of carrierscompared with the single carrier that is needed for quantum operations.Doped semiconductor layers have even more carriers and thus are lessattractive for single electron operation.

To achieve single carrier behavior in semiconductor layers it ispreferable to first deplete them of carriers before performing thesingle electron operations. It is relatively easy to deplete anintrinsic (i.e. undoped) semiconductor and even a low dopedsemiconductor. Depleting a higher doped semiconductor layer is harderand requires much larger potentials to achieve depletion. Furthermore,it is easier to deplete a thin layer of semiconductor than it is todeplete a thick layer of semiconductor. Thus, for building semiconductorquantum structures based on single electron behavior, an SOI processhaving a thin top active layer and an oxide layer to isolate the toplayer from the substrate is preferred.

In such processes, the body of the devices is relatively easy to fullydeplete. In most cases even the work function between the gate and thethin active layer is enough to generate a full depletion of the thinlayer. In other cases a certain gate voltage may be needed to fullydeplete the body of the device. In fully depleted processes, the thinsemiconductor layer is depleted of free carriers due to the presence ofone or more control gates on top.

Once the semiconductor layer is fully depleted, there are no other freecarriers that can interact with the quantum particle(s) and quantumeffects can come forth. In a fully depleted well (which may haveinitially been undoped or low doped), the potential on the control gateson top determines the its profile. Such potential profile may, forexample, have valleys and peaks. The valleys is where a carrier may belikely located and the peaks constitute tunneling barriers that mayprevent the particle(s) from moving from one position to another.

In such a fully depleted semiconductor layer (CAD drawn layer may beundoped or low doped) a single carrier (e.g., electron) may be injectedusing an interface device. The particle may be trapped in a givenlocation in the depleted well where the potential has a valley boundedon both ends by tunnel barriers. By appropriately changing the controlsignals on the gate, the potential in the well and the heights of thebarriers can be modified and thus the single particle may move from onelocation to another in the fully depleted well. This is the basis of theoperation of the charge/position quantum qubit.

Classic FET transistors, on the other hand, have higher doped regionsfor the source and drain. In bulk processes, the higher doped source anddrain regions are formed directly in the body well by implanting ordiffusing dopants. In fully depleted SOI processes where a thinsemiconductor film is deposited on top of the BOX oxide that providesisolation from the substrate, the source and drain regions are realizedby depositing another layer of high doped semiconductor on top of theundoped thin layer.

The interface devices have on one side of the gate a higher doped layerthat behaves classically and carriers that behave collectively, whileunder the gate and on the opposite side thereof is the original undopedlayer which is fully depleted. The gate terminal determines the heightof the tunnel barrier and may allow a single particle to be injected inthe fully depleted well. The particle will be localized in the fullydepleted well in a region where a valley of the potential is present.From this point on a quantum operation may be performed on the singlecarrier that was separated from the classic collectivity of carrierspresent on the classic well of the device.

Half Classic/Half Quantum Interface Device and Example Structures

The interface device disclosed herein is operative to provide a linkbetween classic electronic circuits and quantum circuits. A well is afairly isolated semiconductor layer that can be part of a device. Aclassic well is contacted with metal layers to other devices and usuallyhas a large number of free carriers that behave in a collective way,sometimes denoted as a “sea of electrons.” A quantum well, however, isnot connected to classic devices that may have a sea of electrons. Thequantum well may or may not have contacts and metal on top, but suchmetal is left floating. A quantum well holds one free carrier at a timeor at most a few carriers that have single carrier behavior.

The ability to inject one single carrier at a time is needed to operatea quantum structure. The charge of a carrier (i.e. electron or hole) is1.6×10⁻¹⁹ Coulomb. The charge is the integral of the current over agiven time interval. Classic devices operate with current that areusually in the 0.1 uA and higher level. If a 0.1 uA current is used toinject a single electron, the pulse width of the current needs to be1.6×10⁻¹² sec. A pulse in the 1 ps range could require clock frequenciesin the THz range if implemented straightforwardly with clocks, which arenot available in current integrated semiconductor processes.Furthermore, the dependence of the transistor current on the appliedvoltage is relatively moderate, e.g., quadratic or even linear. Thus, inorder to stop the current flow a large voltage difference is required.Such a voltage is much larger than what a typical Coulomb blockadevoltage is in currently available semiconductor processes.

To stop the flow of current with a Coulomb blockade voltage, the currentdependence on the voltage needs to be very steep, e.g., exponential.Such current to voltage dependencies are achieved in deep subthresholdregimes when a tunneling current is present in the device.

To inject a single electron with a pulse in the 100 ps range requires acurrent of 1 nA. Such a current puts the small nanometer devices in deepsubthreshold mode of operation. In this regime a tunnel current withexponential voltage dependence is established between the twowells/sides of the device.

In classic electronic circuits operating at room temperature if theinterface device generates a 1 nA current multiple carriers (i.e.electrons) will be transferred to the second well provided that a closedpath is established for the device current. If the second well isconnected electrically, there is no force that will oppose the flow ofadditional carriers in the second well. When the second well is leftfloating, a different behavior is ensured.

To achieve quantum operation the devices are cooled down to deepcryogenic temperatures such that the thermal noise or thermal agitationof the carriers is minimal. Also, the quantum devices need to usedimensions in the nanometer range, such that the capacitance of thestructure is in the 100 aF range. In such cases the Coulomb blockadevoltage becomes multi-millivolt level. This is needed since thetransport of a single carrier from the classic well to the quantum wellrequires a change of potential (Coulomb blockade) large enough that thetunnel current is reduced significantly and no further carrier willtunnel to the quantum well. The dependence of the tunnel current on thepotential difference between the gate and the well is exponential.Therefore, voltage changes of a few to tens of millivolts can readilystop the further tunneling of subsequent particles.

In a half-classic, half-quantum interface device the Coulomb blockadegenerated by the tunneling of a single carrier to the quantum wellprevents other carriers from tunneling. In order to establish theinitial tunneling current from the classic well to the quantum well, apotential difference is established between the well and the controlgate. In one embodiment, the interface device is realized by placing acontrol gate over a continuous well. The potential of the gate which isdirectly driven or has its potential imposed for example by a capacitordivider such that a depletion region is established under the controlgate thereby separating the well into two sections: one classic and onequantum. The classic well is connected to other classic devices usingmetal layers. In order to control the device with the gate signal, thepotential of the classic well needs to be set at a certain referencevalue. This is done with a classic FET transistor that resets thepotential of the classic well during a rest time period.

With the classic well sitting at a V_(classic_ref) potential, thepotential of the gate is changed by a control signal such that asubthreshold tunnel current is generated in the interface device. Thesign of the gate potential depends on the doping type, the level of thewell, and the material of the gate and oxide which in turn set the workfunction difference. In the case of a P−type well the gate voltage needsto be more positive than the classic well potential, assuming a zerowork function difference.

In this manner a pulse signal applied at the gate of the interfacedevice determines the tunneling of precisely one particle (e.g.,electron) from the classic to the quantum well. The pulse duration doesnot need to be very precise. It just needs to be longer than what isneeded to securely tunnel a single particle. No further particle will betunneled, even though the pulse may be longer because of the Coulombblockade voltage that will exponentially reduce the tunnel currentlevel.

Once a single carrier (e.g., electron or hole) is injected into thequantum well, a pure quantum operation can be performed. Usingadditional control gates on top of the continuous well which furtherisolates quantum dots in the structure, the carrier may be transportedin a discrete fashion from one qdot to another. If appropriate controlsignal pulse widths are applied, the particle (actually, itswavefunction) may be split between two or more qdots. In one embodiment,a quantum structure can have a plurality of wells with a plurality ofqdots. If the wells are brought in close proximity at least in a certainlocation, interaction (i.e. entanglement) between quantum particles canoccur.

In one embodiment, a quantum structure comprises one or morehalf-classic, half-quantum interface devices. Each interface deviceinjects a single carrier or multiple carriers but at different timeinstants, with one carrier at a given time.

The gate-to-classic well potential difference needed to realize thetunneling of the single carrier varies with process and location of thedevice. It also varies with the temperature of the structure. Tomitigate such variability, the gate control signal has adjustabilitybuilt-in such as via a digital to analog converter (DAC) and acalibration engine to set the appropriate voltage level for eachindividual injection device (i.e. half-classic, half-quantum interfacedevice).

A diagram illustrating a first example interface device of the presentinvention in more detail is shown in FIG. 10A. The device, generallyreferenced 802, comprises a conventionally doped diffusion region 812and one or more metal contacts 814, gate 806 and gate contacts 804, anda non-doped (intrinsic or no diffusion) or very low doped (n−−, p−−)region 820 having no or low n− or p− doping, diffusion, and no contactsnor metal. The doped diffusion region 812 is either low doped (n−, p−),medium doped (n, p), high doped (n+, p+), or highly doped (n++, p++).The doped semiconductor side 812 of the gate 806 connects to classicalsemiconductor electronic circuitry 816, which can comprise a particle(e.g., electron) injector controller, a gate imposer controller, and aparticle detector in addition to various other control, detection andprocessing functionalities (see FIG. 2). The gate 806 can also connectto the circuitry 816 (not shown). The non-doped side 820 of the gate 806connects to quantum semiconductor circuits 818. Thus, half the devicecontains classic carriers in energy bands and the other half containsquantum carriers in discrete energy levels. The transport of carriersfrom the classic side to the quantum side of the device is realizedthrough tunneling through highlighted region 808. An appropriatepotential applied to the gate is operative to connect a particle fromthe quantum side to the classic side of the interface device. This way,the quantum particle can electrically join the potential sea ofcarriers. Note that the labels ‘quantum side’ and ‘classic side’ are forconvenience sake since at the fundamental level there is nothinginherently quantum or classic with the two sides of the gate.

In operation, the interface device 802 functions to provide an interfacefrom conventional electronic circuitry located on (or off) theintegrated circuit to quantum circuits and vice versa. In particular,the interface device is operative to separate a single quantum particle824, e.g., electron, etc., from a plurality of particles 822. A singlequantum particle is allowed to tunnel (indicated by arrow 810) throughthe depletion region 808 in an injector mode of operation. Anappropriate gate control signal is applied to the gate 806 to establishthe energy barrier and to control the tunneling through the depletionregion. Note that an appropriate potential might need to be set on dopedregion 812 prior to this operation. Thus, the interface device functionsas an injector tunneling device that allows the tunneling of a singlequantum particle, or alternatively a controllable number of particles.When the gate potential is carefully lowered, a single quantum particle(e.g., electron) is allowed to tunnel from the left to the right side ofthe device.

In addition, in one embodiment, the logical flow of electrons can beprovisioned to function in the opposite direction whereby the interfacedevice is part of a circuit that senses and detects the presence of asingle particle. In this case, the interface device can serve as thesensor which is coupled to additional classical circuitry (not shown) todetect the presence of single particles. In particular, if thecapacitance on the classic side of the device is sufficiently lowenough, the presence of a single particle (e.g., electron) on thequantum side of the device can be sensed or detected on the classicalside of the device using conventional electronic circuitry, such as 816.This is achieved by detecting the rise in voltage magnitude on theclassical side caused by the presence of the single particle on thequantum side upon lowering the barrier of the gate 806. Thus, theinterface device is capable of operating bidirectionally as both aninjector of a single particle and a detector of a single particle.

Note that in operation, on the classic side of the interface device, thequantum particles, e.g., electrons, are in energy bands, i.e. conductionband and valence band, which enables current flow in classicsemiconductor devices. On quantum side of the interface device, thequantum particle is in discrete energy levels with one or two electrons(spin up and down) in each level.

A diagram illustrating a second example interface device of the presentinvention is shown in FIG. 10B. It is appreciated that the interfacedevice can have many shapes depending on the particular implementationof the invention. In this example, the interface device, generallyreferenced 830, has an ‘L’ shape and comprises a conventionally low,medium, high, or highly doped region 838 with one or more metal contacts836, gate 834 and gate contacts 832, and a smaller non-doped (intrinsic)or very low doped region 839 without n+ or p+ doping, contacts, ormetal. Note that the ‘L’ shape helps provide shifting on the y-axis andthus increases the distance from other structures.

A diagram illustrating a third example interface device of the presentinvention is shown in FIG. 10C. In this example, the interface device,generally referenced 840, has a diagonal shape and comprises aconventionally low, medium, high, or highly doped region 848 with one ormore metal contacts 846, gate 844 and gate contacts 842, and a smallernon-doped (intrinsic) or very low doped region 849 with n−− or p−−doping.

A diagram illustrating a cross section of a first example semiconductorquantum structure and conventional FET is shown in FIG. 11. Thestructure, generally referenced 850, comprises a conventional classicFET on the left, a fully quantum device on the right, and a halfclassic/half quantum interface device in the middle. All three devicesare fabricated on substrate 852 and oxide layer 854. It is appreciatedthat other types of substrates are possible as well.

The classic FET on the left comprises source, drain, and gate includingp or n doped well 878, 861 connected to contact 858 and metal 856structures located on either side of metal or polysilicon (or metal)gate 860 built over oxide layers 851, 853. In classic FET operation,mobile carriers travel from source to drain through inversion channel855 in accordance with the potential applied to the gate, source anddrain terminals. Note that the inversion channel may be pinched whereincarriers are swept by the electric field through the pinched area.

The fully quantum device on the right comprises two qdots in well 879separated by metal or polysilicon gate 864 and oxide layers 870, 872over depletion region 868. The gate modulates tunneling (arrow 869)between the two qdots as described in detail supra. Note that the twoqdots on either side of gate 864 have no diffusion, contacts or metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 862 and oxide layers 870, 872 over depletionregion 866. The gate modulates tunneling (arrow 867) to allow a singlequantum particle to tunnel between doped region 878, 874 on the leftside of the gate 862 and the qdot on the right side of the gate. Thehalf classic/half quantum interface structure thus functions to providean interface mechanism between classic electronic circuitry on the leftand quantum circuitry on the right.

A diagram illustrating a cross section of a second example semiconductorquantum structure and conventional FET is shown in FIG. 12. Thestructure, generally referenced 880, comprises a conventional (i.e.classic) FET on the left, a fully quantum device on the right, and ahalf classic/half quantum interface device in the middle. All threedevices are fabricated on substrate 892 and oxide layer 894.

The classic FET on the left comprises source, drain, and gate includingdoped well 882, 918 connected to contact 916 and metal 896 structureslocated on either side of metal or polysilicon gate 898 built over oxidelayers 910, 912. In classic FET operation, mobile carriers travel fromsource to drain through inversion channel 914 in accordance with thepotential applied to the gate, source and drain terminals.

The fully quantum device on the right comprises two qdots in well 908separated by metal or polysilicon gate 900 and oxide layers 902, 904over depletion region 887. The gate modulates the tunneling (arrow 886)between the two qdots as described in detail supra. Note that the twoqdots on either side of gate 900 have no diffusion, contacts or metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 899 and oxide layers 902, 904 over depletionregion 885. The gate modulates the tunneling (arrow 884) between theregion on the left of the gate to the region on the right. In thisembodiment of the interface device, the doped region 918, 906 of drainof the classic FET is moved closer to the gate 898 and a non-diffusionregion is inserted on the left side of the gate 899 in order to reduceparasitic capacitance. The half classic/half quantum interface devicefunctions to provide an interface mechanism between classic electroniccircuitry on the left and quantum circuitry on the right.

A diagram illustrating a cross section of a third example semiconductorquantum structure and conventional FET is shown in FIG. 13. Thestructure, generally referenced 920, comprises a conventional (i.e.classic) FET on the left, a fully quantum device on the right, and ahalf classic/half quantum interface device (i.e. interface device) inthe middle. All three devices are fabricated on substrate 922 and oxidelayer 924.

The classic FET on the left comprises source, drain, and gate includingdoped well 938, 936, 954 connected to contact 928 and metal 926structures located on either side of metal or polysilicon gate 930 builtover oxide layers 942, 944. In classic FET operation, mobile carrierstravel from source to drain through inversion channel 940 in accordancewith the potential applied to the gate, source and drain terminals.

The fully quantum device on the right comprises two qdots in well 956separated by metal or polysilicon gate 934 and oxide layers 946, 948over depletion region 962. The gate modulates tunneling (arrow 964)between the two qdots as described in detail supra. Note that the twoqdots 950, 952 on either side of gate 934 have diffusion but no contactsor metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 932 and oxide layers 946, 948 over depletionregion 960. The gate modulates tunneling (arrow 958) between thediffusion region 936, 954 on the left side of the gate 932 and well 956with diffusion 958 on the right side of the gate. The half classic/halfquantum interface device functions to provide an interface mechanismbetween classic electronic circuitry on the left and quantum circuitryon the right. Note that in one embodiment, similar structures can bebuilt using bulk processes with no oxide layer under the quantumstructure but with a depletion region instead.

As described supra, the quantum processor of the present inventioncomprises a mix of structures including quantum structures,conventional/classic FET structures, and interface devices comprisinghalf classic and half quantum operation which are used to moveinformation from the conventional FET (i.e. non-quantum) domain to thefull quantum domain.

A diagram illustrating an example quantum structure with interfacedevices is shown in FIG. 14. The example structure, generally referenced670, comprises a middle full quantum structure (dashed circle 683)having gate 689 sandwiched by a left side interface device structure(dashed circle 681) with gate 674 and a right side interface devicestructure (dashed circle 685) with gate 676. The interface devices 681,685 comprise a conventional FET (darkened areas 684, 687) on one side oftheir gate and quantum device on the other side.

The structure 670 comprises two qdots and utilizes well-to-welltunneling through local depleted region. An interface device is locatedat each end for interfacing with conventional electronic circuits. Thepotential on the control gate can be applied either with a directvoltage drive network or via a floating impedance division. The well isrealized with two rectangular wells having an overlap to create thenarrow tunneling channel 671.

A diagram illustrating a first example multiple qdot quantum structurewith interface devices on either end thereof is shown in FIG. 15A. Thehigher complexity semiconductor quantum structure, generally referenced690, comprises a continuous well with a plurality of imposing controlgates 696 and gate contacts 692 that separate it into a plurality ofqdots 698. In this example, the well comprises a plurality ofoverlapping squares connected at their corners to create a narrow tunnelpath 699. Located at either ends of the well are interface devices 694that allow the connection of the reset, injection and detectioncircuits. The imposer gates 696 receive pulsed control signals thatdetermine the specified quantum operation.

A diagram illustrating a CAD layout of an example quantum structure isshown in FIG. 15B. The layout, generally referenced 700, comprises acontinuous well with a plurality of control gates 706 and gate contacts704 that form a plurality of qdots 702. In this example, the wellcomprises a plurality of abutting squares connected at their edges tocreate a tunnel path. Located at either ends of the well are interfacedevices 708 with contacts 709 that allow the connection of the reset,injection and detection circuits (not shown). Note that these threecircuits can be all electrically connected to the same node, forexample, 812 in FIG. 10A.

A diagram illustrating a cross section of the quantum structure of FIG.15A is shown in FIG. 16. The quantum structure has multiple qdots withinterface devices at both ends of the well. The single continuouslydrawn well is separated into a plurality of qdots by the local depletionregions induced by a plurality of control gates. The cross section 710comprises a substrate 712 and oxide layer 714 on which are fabricatedseven qdots 722 comprising six control gates 722 each including oxidelayers 728, 730, and polysilicon or metal layer 726, two interfacedevices 720 each including n or p doped regions 718, 716, contact 711,and metal layer 713, and gate 732.

To illustrate the operation of the quantum structure of the presentinvention, a series of diagrams are presented that show the stepsinvolved in an example quantum operation starting with a single quantumparticle where the local depletion region is under control of the gate.

A diagram illustrating the aperture tunnel barrier for a two quantum dotstructure is shown in FIG. 17A. The local depletion region under thecontrol gate divides the structure into two qdots, namely a left qdotstorage 741 and a right qdot storage 743. The tunnel barrier imposed bythe local depletion region is represented by trace 740. In this phase,the depletion region is wide and the tunnel barrier is high (referenced742) and the particle 746 cannot tunnel to the right qdot storage and istrapped in the left qdot storage.

A diagram illustrating a first example change in the aperture tunnelbarrier for the two quantum dot structure is shown in FIG. 17B. Thetunnel barrier imposed by the local depletion region is represented bytrace 744. In this phase, an appropriate potential is applied to thecontrol gate to cause the depletion region to narrow thus lowering thetunnel barrier (referenced 745). This permits the particle 748 to travelto the right qdot storage and the particle is in the left and rightqdots at the same time.

A diagram illustrating a second example change in the aperture tunnelbarrier for the two quantum dot structure is shown in FIG. 17C. Thetunnel barrier imposed by the local depletion region is represented bytrace 750. In this phase, the potential applied to the control gate isadjusted to cause the depletion region to widen again thus raising thetunnel barrier (referenced 752). This effectively traps the two splitparticles 747, 748 (i.e. the wavefunction of the particle is split) andprevents them from traveling from one qdot to the other through thetunnel barrier. In quantum fashion, the charge carrier is split betweenthe two qdots. When performing detection, however, the carrier will onlybe on one side with a corresponding probability.

Thus far only electric control of semiconductor quantum structures hasbeen presented wherein the spin of the quantum particle is ignored. Analternative manner of controlling the semiconductor quantum structure isto control/select the spin of the quantum particle using a magneticfield from an inductor/coil or a resonator. A property of particles isthat they tend to align their spins to any external relatively strongmagnetic field. A diagram illustrating an example quantum structuresurrounded by a spin control magnetic coil is shown in FIG. 18.

The structure, generally referenced 760, comprises a resonator 763 orone or more turns of a coil 762 surrounding a continuous well dividedinto two qdots 764 by control gate 766 and connected by tunnel path 768.Along with the electrical control of the imposing gate, this structurealso uses the magnetic field generated either by (1) an inductor 762 or(2) a resonator 763 that surrounds the entire quantum structure toselect the spin of the particle. Note that both are shown in the figurebut in practice typically only one is implemented. Note also that bothstatic and ac magnetic fields can be generated and used. In addition,the inductor may overlap only a local area including one or severalquantum structures or it can overlap the global area where the quantumcore is implemented. In this manner, local magnetic control or globalmagnetic control can be implemented.

As described supra, the quantum computer operating environment employscooling at cryogenic temperatures. In addition, electric and magneticfield shielding is provided. The cryostats used typically compriserelatively large metal structures that act as good shields. In oneembodiment, the metal cavity of the cryostat creates a high qualityresonator that generates a magnetic field to control the semiconductorquantum structures at its interior.

A diagram illustrating a second example multiple qdot quantum structureis shown in FIG. 19. The structure, generally referenced, 770, comprisesa blended continuous well path 772 overlapped by a plurality of controlgates 776 with contacts 774 (three in this example). Here the width ofthe vertical segments of the control gates and the vertical andhorizontal segments of the well are the same, i.e. a “boomerang”structure in which the width of the wider well regions is made equal tothe width of the narrow channel links. Such a structure results in amore compact realization of the quantum structure. Note that the regionsbetween control gates form the quantum dots, while the regions under thecontrol gates realize the induced depletion regions through whichtunneling occurs. It is appreciated that any number of qdot structurescan be realized depending on the number of control gates implemented.Note that in one embodiment, such structures can be implemented usingeither planar or 3D semiconductor processes.

A diagram illustrating a third example multiple qdot quantum structureis shown in FIG. 20. In an alternative embodiment, the semiconductorstructure comprises a bended well path overlapped by gates usinghorizontal and inclined well segments. Note that vertical segments alsopossible. In particular, the structure, generally referenced, 780,comprises a blended continuous well path 782 overlapped by a pluralityof control gates 786 with contacts 784 (three in this example) usinghorizontal and inclined well segments. Here too the width of thevertical segments of the control gates and the vertical and horizontalsegments of the well are the same, i.e. a “boomerang” structure in whichthe width of the wider well regions is made equal to the width of thenarrow channel links. Such a structure results in a more compactrealization of the quantum structure. Note that the regions betweencontrol gates form the quantum dots, while the regions under the controlgates realize the induced depletion regions through which tunnelingoccurs. It is appreciated that any number of qdot structures can berealized depending on the number of control gates implemented.

A diagram illustrating a fourth example multiple qdot quantum structureis shown in FIG. 21. In an alternative embodiment, the semiconductorstructure comprises a bended well path overlapped by gates usinghorizontal and rounded well segments. Note that vertical segments alsopossible. In particular, the structure, generally referenced, 790,comprises a blended continuous well path 792 overlapped by a pluralityof control gates 796 with contacts 794 (three in this example) usinghorizontal and rounded well segments. Note that the regions betweencontrol gates form the quantum dots, while the regions under the controlgates realize the induced depletion regions through which tunnelingoccurs. It is appreciated that any number of qdot structures can berealized depending on the number of control gates implemented.

Quantum State Detection

In semiconductor quantum structures and circuits, the qubits (i.e.elementary quantum information units) are encoded by the state ofparticles or carriers inside one or more semiconductor layers. To helpto achieve the single carrier behavior, the semiconductor layers areusually fully depleted. In the case of spin qubits the detectionincludes determining the spin orientation of a given carrier (e.g.,electron or hole), while in the case of charge qubits (i.e. positionqubits) the detection includes determining if the carrier is present ornot in a given qdot.

Classically, a bit can have only two values “0” and “1”. In the quantumdomain, however, a qubit can have a large number of values given by anyconstrained combination of the two base quantum states |0> and |1>. Thisis provided by the superposition character of the quantum states.

When a quantum state is detected, the quantum state is collapsed into abase state which corresponds to a classic state with a given probabilityassociated with it. For example, in the detection of a charge qubit, theoutcome can be either: (1) the carrier is present in the detection qdotwhich corresponds to the base state |1>; or (2) the carrier is notpresent in the detection qdot which corresponds to the base state |0>.To determine the value of a quantum state, a number of successivequantum experiments are performed to get the average presenceprobability of the detected carrier. By computing the number of |0>s and|1>s that are obtained in the detection, the probability of the quantumstate is determined.

For example, consider the Hadamard equal distribution quantum statedenoted by 0.707|0>+0.707|1> where the carrier is split equally into twoqdots of the quantum gate. From the quantum perspective, this means thecarrier is present simultaneously in both qdots. In the classic view,the electron cannot be split and it either is present in a given qdot orit is absent from that qdot. When detecting a Hadamard state multipletimes it is expected to obtain an equal number of collapses to the |0>base state (i.e. the carrier is absent) and to the |1> base state (i.e.the carrier is present) in the detected qdot. If the quantum state has agiven rotation and it has a larger |1> base state component (a|0>+b|1>with b>a) then at detection more collapses to the base state |1> shouldoccur. If in contrast, the quantum state has a rotation towards the |0>base state (a|0>+b|1> with a>b) then more collapses to the base state|0> should occur.

In order to perform detection of a quantum state contained in a quantumdevice, the quantum structure is connected to classic devices. This isachieved using an interface device, described in detail supra. Suchinterface devices are half-quantum and half-classic in their nature orinterpretation. In one embodiment, the detector circuit itself comprisesclassic devices that process charge, current, and voltage. The quantumdevices operate with single carrier (e.g., electron or hole), or a smallcontrollable number thereof, while the interface device extracts asingle carrier from a sea of collective electrons in the classic worldor vice versa injects a single carrier into a classic world sea ofcollective carriers.

In one embodiment, the classic device of the detector is connected at aquantum structure using a floating well, in which the interface devicehas a quantum well on one side and a floating classic well on the other.Since the classic well is set to be floating, the injection of a singlecarrier may result in a noticeable well potential change that can beamplified further.

In another embodiment, the classic device of the detector is connectedat a quantum structure using floating gate detection. In this case, theinterface device is realized by a device having a plurality of gates,one of them being shared with a classic FET detector device. When thecarrier arrives under the floating gate of the interface device itchanges the potential of the gate, which in turn can be measured by theclassic FET of the detector which shares the gate with the interfacedevice.

Floating Well Detection

In floating well detection, the quantum particle is injected from thequantum device (if it happens to be present there) into a classicfloating well that is in turn connected to the input of the classicdetector circuit. An equivalent schematic of the quantum circuit,generally referenced 990, together with its associated interface andclassic circuits is shown in FIG. 22A. A top plan layout view of thecircuit is shown in FIG. 22B and a cross section of the circuit is shownin FIG. 22C. The quantum circuit 990 comprises several layers includingsubstrate 1010, BOX oxide 1008, and undoped fully depleted layer 1006.Doped regions 1020 are fabricated over the fully depleted layer.

In one embodiment, before starting a quantum operation, the entirequantum structure is reset, i.e. the entire quantum well is flushed ofany free carriers. Since the quantum well is fully depleted, there areno carriers in it. A reset operation is performed by one or more classicMreset devices 992 by appropriately controlling the interface quantumgates (Qinterface) 994 and imposer quantum gates (Qimp) 996. The classicMreset device comprises metal contacts 1002 on its terminals realized bydoped semiconductor layers 1020. Considering the SOI semiconductorprocess as an example, the source and drain doped diffusions arefabricated above the undoped fully depleted device body 1006. The Mresetdevice establishes a reference potential for the classic side of theclassic to quantum interface device on the left. During the quantumoperation it is assumed that this potential does not change much due toleakage currents.

In one embodiment, quantum operation begins by initially resetting theclassic well to a reference potential then setting it floating duringthe detection time interval. A single carrier (e.g., electron or hole,if one happens to be present there) is injected from a classic well 1022where a sea of carriers have a collective behavior, into a quantum well1024 where single carrier behavior can occur. An appropriate potentialis applied to the gate 1004 of the Qinterface device 994 to control thetunneling of a single particle 1012 to the quantum side by lowering thetunneling barrier. Once the single particle is injected into the fullydepleted well 1024, it moves according to the potential distributionchange determined by the plurality of quantum imposing gates (Qimp) 996.In one embodiment, the Qimp gates determine the creation of valleys inthe potential distribution that is progressively shifted from left toright and thus determine the movement of the particle 1012. Depending onthe timing and pulse widths of the Qimp signals, a carrier may be splitbetween different locations in the fully depleted well in which two ormore potential valleys may be realized. This is the base of generatingthe superposition quantum states (a|0>+b|1>).

At the opposite end of the well, a second interface device 998 providesthe interface in the other direction from the quantum well 1026 to theclassic well 1014. In one embodiment, the classic well is left floating(no dc path to ground) such that the potential injection or transfer (byvirtue of the connecting transistor 998) of a single carrier cangenerate a measurable change in potential that is further processed bythe detector classic circuit 1000. Since the particle is injected (ortransferred) from the quantum well into a classic well, the quantumstate collapses. This detection is destructive since the quantum stateis destroyed during the measurement process. It is destroyedspecifically during the instance the particle sees a low resistancepath, i.e. is connected, to the sea of carriers on the classic side. Itis noted that such destructive detection can be performed only once perquantum operation. Furthermore, it is noted that another reset devicesimilar to 992 can be connected to the same node 1014 as that connectedto the detector 1000. Likewise another detector similar to 1000 can beconnected to the reset device 992 (node 1003). These two types ofcircuits operate in a time shared manner in which the active time slotsallocated to them can be different. Their high resistance during theinactive time slots ensures no conflicts.

The floating classic well 1014 is connected to the gate 1016 of adetection device 1000. The floating well and the gate 1016 of thedetector Mdetector have a certain total capacitance. The voltage changein the signal at the gate 1016 of Mdetector is given by ΔV=e/C where eis the carrier charge 1.6×10⁻¹⁹ Coulomb and C is the total capacitanceof the floating well (1014 and possible 1026) and gate. In oneembodiment, the charge to voltage conversion is followed by classicvoltage or transconductance amplifiers depending on the voltage mode orcurrent mode operation of the classic detector circuit 1000. Note thatthe entire single carrier (e.g., electron) injection, quantumprocessing/imposing and detection is short in comparison with thedecoherence time of the particle in the given semiconductor structure.

Note that other classic analog, mixed signal or digital circuits arepreferably kept an exclusion distance away from the quantum structure990 in order to avoid undesired parasitic interaction with the quantumparticle(s) that could lead to quantum decoherence.

Floating Gate Detection

The second option for the detection of the quantum state is to use afloating gate. In this case the classic device of the detector Mdetectoris connected to the same floating gate that goes over the quantum well.An equivalent schematic of the quantum circuit, generally referenced1030, together with its associated interface and classic circuits isshown in FIG. 23A. A top plan layout view of the circuit is shown inFIG. 23B and a cross section of the circuit is shown in FIG. 23C. Thequantum circuit 1030 comprises several layers including substrate 1050,BOX oxide 1048, and undoped fully depleted layer 1046. Doped regions1058 are fabricated over the fully depleted layer.

Similar to the floating well detection circuit 990 described supra, thequantum procedure starts with the reset of the structure 1030 using oneor more classic Mreset devices 1032 along with appropriate control ofthe interface quantum gates (Qinterface) 1034 and imposer quantum gates(Qimp) 1036 such that all free carriers in the quantum structure areflushed out. The classic to quantum Qinterface device 1034, operative toinject a single carrier 1052 into the quantum structure, has ahalf-classic and half-quantum operation. It comprises a doped and metalcontacted classic well 1054 on the left side of its gate 1044 and afloating quantum well 1056 on the other side. In one embodiment, theconnection between the Mreset and Qinterface devices on the classic sideis realized with contacts and metal layers 1055. Note that the Mresetand Qinterface devices may share the same active layer or may be done inseparate active layers.

The quantum imposer (Qimp) devices 1036 determine the specific quantumcomputation performed. There is at least one Qimp quantum control gate.Alternatively, the circuit may comprise any number of Qimp devices aslarge as feasible in the actual implementation using a givensemiconductor process.

The last three gates over the quantum well on the right side of thecircuit 1030 form a quantum to classic Qinterface device 1038, 1064,1062. Note that alternatively, the Qinterface device may be located inthe middle of a quantum well. One of the three gates (1060) is thefloating gate which connects to the Mdetector classic detector device1040. In one embodiment, the carrier is moved under the floating gate bycontrolling the potential distribution with the two adjacent gates 1059,1061. The presence of the quantum carrier under the floating gate causesa change of the potential of the quantum gate which is sensed by theMdetector detector device 1040 and amplified further.

After the first measurement is performed, the quantum carrier can bemoved away from under the floating gate 1060 of the interface device.The floating gate initial potential is set during the reset time to alevel that allows the proper operation of the Mdetector classic detectordevice. Such potential may be reset for example with a second classicMreset device (not shown) connected to the gate of the Mdetector device.

An example potential diagram for the floating gate detection circuit isshown in FIG. 24. The last quantum imposer gate Qimp 1076 together withthe three gates 1077, 1078, 1079 of the quantum to classic interfacedevice (Qinterface) 1070 are shown. In this example, two ‘helper’ gates(left gate 1077 and right gate 1079) are controlled and not floatingwhile only the middle gate 1078 is floating and used for actualdetection. The middle floating gate 1078 is connected to the detectorcircuit 1040 (FIG. 23A). It is appreciated that the Qinterface devicemay comprise more or less than three gates. For example, the detectioncan be performed using only two interface device gates, i.e. onefloating and one controlled.

In operation, the particle is moved one or more times under the floatinggate to perform detection (i.e. nondestructive measurement). Multiplemeasurements are performed under the detection gate for the same quantumexperiment. A measurement is made each time the particle moves under thefloating gate 1078. Note that the movement is speculative in naturesince it is not known a priori whether there is a particle present ornot as this is what is being measured. If no particle is detected, thenof course no movement actually takes place.

With floating gate detection, a gate overlaps the last region of aquantum well where the presence of a particle is to be detected. Notethat the potential of the floating well can be set initially, forexample during the reset process, to a reference value appropriate forthe detector circuitry. It should, however, be subsequently allowed tobe floating such that it can sense the presence or absence of a particleunder it, e.g., carrier, electron, hole, etc.

In the floating gate detection process the quantum state or qubit isallowed to move under the floating gate. If a particle is present thanthe potential of the gate changes from the reference potential it wasinitially set to, while the particle is not present than the potentialof the gate does not change due to the quantum state moving under thegate.

Note that in idealized circuits there are no parasitic leakage currentsand the potential of a floating gate can remain for relatively longperiods, ideally to infinity or until it is again reset to the potentialit achieved at the end of processing. In real circuits, however,parasitic leakage currents typically exist (e.g., a gate over a well mayhave a certain leakage current from the gate to the well). Such currentchanges the potential of the floating gate independent of the presenceor absence of the quantum particle.

To prevent such floating gate potential change due to leakage, numerouswell-known circuit techniques can be applied, including performing thedetection quickly such that there is not enough time for the floatinggate potential to change significantly due to leakage. In this case asignificant potential change is a fraction of the potential changedetermined by the presence of the quantum particle, e.g., 10% or 20%.Another technique is to use a replica floating gate that never gets aquantum particle but has similar leakage current with the detectionfloating gate. By measuring the differential signal between thedetection floating gate and the replica floating gate, the voltagechange due only to the presence or absence of the quantum particle canbe detected, while any parasitic voltage change due to leakage currentis rejected as a common mode signal.

In one embodiment, the actual operation of the floating gate detectionconsists in modifying the potential in the proximity of the floatinggate such that the quantum particle is moved in a controlled fashionunder the floating gate and then away from it.

Since the quantum particle can be moved multiple times under thefloating gate and then away from it, this detection is non-destructiveand can be performed multiple times. By performing the detectionmultiple times any parasitic effect due to inherent noise in the systemis eliminated or attenuated. Note that the number of consecutivenon-destructive detections that can be performed, however, depends onthe decoherence time of the quantum state in the given processtechnology and given physical structure.

With reference to FIG. 24, to impact the potential around the floatinggate and thus allow the quantum particle to move under the floating gateand then away, multiple additional helper control gates are used. In oneembodiment, a single helper control gate is used located on one side ofthe main floating detection gate. In another embodiment, two helpercontrol gates are used, one on each side of the main detection floatinggate, as shown. Alternatively, additional helper control gates can beplaced around the main detection floating gate. The further away thehelper gate is placed, however, the less impact it has on the potentialprofile around the detection floating gate. This is why the mosteffective are the helper gates directly to the left and right of themain detection gate.

A quantum structure includes a number of control gates, also calledimposers that determine the specific quantum operation performed. Afterthe last imposer has performed its function, the desired quantumcomputation has finished and the quantum state is ready for detection.

In position based semiconductor quantum structures the detection entailsdetermining whether or not the particle is present in the last quantumdot of the structure, past the last imposer. If the quantum state is oneof the base states, i.e. particle present or absent, then the detectioncan be done only once (in the absence of system noise). When noise ispresent, multiple detections may be desired to reject or attenuate theimpact of the system noise.

If the quantum state is a general superposed state, the particle has acertain probability of being present in the last detection quantum dot.To measure the quantum state, the detection is performed multiple times.The percentage of positive (i.e. present) outcomes versus the totalnumber of measurements represents the probability corresponding to themeasurement of the corresponding quantum state. Similarly, thepercentage of negative (i.e. absent) outcomes may be used.

In trace (A) the control signals on the left and right helper controlgates are such that the energy profile is high and the quantum particleis not allowed to move towards the floating detection gate. Theparticles flow towards the positions with lower energy. If a potentialprofile is drawn instead, the electrons go to higher potential levellocations. The situation is reversed for the holes that go to theregions of higher energy. From the potential perspective, the holes goto the lower potential levels.

Trace (B) illustrates the case when the control signals on the left andright helper control gates are modified such that the energy profilelevel is lowered (1080) in the area surrounding the floating detectiongate. This allows the quantum particle to extend over the entirephysical location where the energy profile is low. This also includesthe region under the floating detection gate.

Trace (C) shows the control signals of the left and right helper controlgates changed such that the region of low energy profile is restrictedto a narrow region essentially under the floating detection gate. Nowthat the quantum particle is localized in a very narrow region under thefloating detection gate. This results in a relatively large (i.e.measurable) change in the potential of the floating gate. When thequantum particle is distributed over a wide area, the change inpotential is much smaller, making it harder to measure. Having theparticle located directly under the floating gate generates a change inpotential of the floating gate which can be measured and amplified bythe Mdetector circuit 1040 (FIG. 23A) using one or multiple classic FETdevices.

The quantum particle is then moved away from the floating detectiongate. As shown in trace (D), first the right helper control gate is usedto enlarge the area of low energy towards the right side, away from thefloating detection gate. In this case the energy profile is still lowunder the floating detection gate which allows the quantum particle tospread both under the floating gate and away from the floating gate.

In a second step as shown in trace (E), the helper control gates areused to raise the energy profile in close proximity of the floatingdetection gate, allowing the quantum particle to extend away from thefloating detection gate. In this manner, the quantum particle is movedaway from the floating gate and the first detection has ended. Thequantum state is still intact. It has not been destroyed through thefirst detection. A second detection may be performed by moving thequantum particle under the floating detection gate again.

Trace (F) shows how the control signals on the two helper control gatesare again enlarging the region with low energy profile, allowing thequantum particle to move again under the floating detection gate. Thelow energy level area remains wide and the quantum particle is spreadboth under the floating detection gate and away from the floating gate.As such the change in potential of the detection gate is low and harderto measure.

In trace (G) the control signals on the helper control gates againdetermine the narrowing of the energy valley where the quantum particleis allowed to spread to a relatively narrow region under the mainfloating detection gate. As such the quantum particle moves a secondtime under the gate and a second non-destructive quantum detection isperformed.

The detection process can continue with multiple subsequent detections.In trace (H) the helper control gates are used to again widen the lowenergy level where the quantum particle is present. In this way thequantum particle is spread under and away from the floating detectiongate.

In trace (I) the helper control gates restrict the area of low energylevel where the quantum particle can be present to a region away fromthe floating detection gate.

In this manner, the process can continue with further subsequentmovements of the quantum particle under the floating detection gate andaway from the floating detection gate, both on the left side and on theright side.

A key advantage of floating gate detection is that it allows multipledetection of the same quantum state, without the need of repeating theentire quantum computation since the particle's wavefunction does notcollapse in the detection process. Therefore, instead of performing theentire quantum experiment multiple times, the quantum experiment isperformed once but the results are measured multiple times. Thisshortens the overall computation time thus increasing the speed ofquantum computation, and thus provides accelerated quantum computation.

In the case of the destructive floating well detection, the quantumparticle is lost with each detection. Thus, performing multiple floatingwell detections require multiple executions of the entire quantumoperation, which in turn takes a longer time. The more time spent ondetection reduces the speed of quantum operation and thus reduces theeffective quantum acceleration factor with respect to a classicalcomputation.

In another embodiment, the floating gate detection may be followed by afloating well detection which finally collapses the quantum state. Byusing both methods of detection, a more sophisticated detection schemecan be built with lower error rate. By looking at the correlationbetween the two types of detection, built-in detection error correctioncan be realized.

3D Semiconductor Quantum Structures

The present invention provides a semiconductor quantum structure thatuses a 3D semiconductor process with very thin semiconductor fins havingmuch smaller parasitic capacitance to the gate. This results in higherCoulomb blockade voltages and thus quantum circuits that are easier tocontrol with classic electronic circuits with more noise floor margin.Two semiconductor islands are isolated in a continuously drawn fin usingan overlapping control gate that induces a local depletion region in thefin. The tunneling between one island in the fin to the other iscontrolled by the control gate that imposes the potential on the fin. Bymodulating the potential applied to the control gate, a controlledfin-to-fin tunneling through the local depletion region is achieved,realizing the function of a position/charge qubit. More complexstructures with higher number of qdots per continuous fin and largernumber of fins can be constructed. 3D semiconductor processes can beused to build such fin-to-fin tunneling quantum structures. Hybrid 3Dand planar structures can be built as well. By combining a number ofsuch elementary quantum structures a quantum computing machine isrealized.

A diagram illustrating an example 3D semiconductor quantum structureusing fin to fin tunneling through local depletion region is shown inFIG. 25. The quantum structure, generally referenced 1840, comprises acontinuously drawn fin 1846, overlapping control gate 1843, two isolatedsemiconductor well and fin structures realize qdots #1 and #2 1842,local depletion region 1848, tunneling path 1841, and particle, e.g.,electron or hole, 1844. A diagram illustrating a three dimensional viewof an example 3D semiconductor quantum structure with fin to fintunneling under control of a control gate is shown in FIG. 26. Thequantum structure, generally referenced 1850, comprises fins withportions 1851, 1853, overlapping control gate 1854, substrate 1855, andlocal depletion region 1852. Note that the well may be omitted and theqdot realized by the semiconductor fin area only.

With reference to FIGS. 25 and 26, the control gate layer overlaps thefin on three sides and creates a local depleted region which isolatesthe two sides when the potential barrier is high. Note that overlappingthe fin provides better control over the structure. A thin oxide layerseparates the semiconductor fin from the control gate. When the controlterminal lowers the potential barrier, tunneling can occur from one sideof the fin to the other side. The tunneling is controlled by the controlterminal that imposes the potential in the semiconductor fin. If thetunnel barrier is high, the quantum particle is locked in its priorstate. When the potential on the control terminal lowers the barrier,the quantum particle can tunnel from one qdot to the other. Depending onthe pulse width of the control signal, the quantum particle completelyor partially tunnels. In the latter case, the quantum particle(precisely, its wavefunction) is distributed between the two qdots, i.e.spatial entanglement. Note that in real implementations, the quantumstructure generally has a deformed complex 3D shape where the depletionregion depends on the particular implementation and semiconductorprocess used. The structures shown herein are for illustration purposesonly.

A diagram illustrating a cross section, side view, and top view of anexample 3D two qdot quantum structure using local fin depletiontunneling is shown in FIG. 27A. The quantum structure, generallyreferenced 1860, comprises substrate 1869, optional oxide layer 1861,wells 1862, 1865, fin 1863, gate oxide 1866, and overlapping controlgate 1864. Note that the dotted line indicates the optional oxide layerthat isolates the 3D quantum structure from the substrate. The substratemay comprise standard resistivity, high resistivity, or isolatingsubstrates.

The tunneling through a local depletion region in the quantum structureis induced in a fin by the overlapping control gate. When the barrier ishigh, the local depleted region is wide and virtually no tunnelingcurrent is allowed. When the barrier is lowered, the local depletedregion shrinks in width and a sizeable leakage tunneling currentappears, which allows the particle to move from one qdot to the other.If the particle has not completed the move from one qdot to the other,it will spread (equally or non-equally) between the two qdots to achievespatial particle entanglement.

A diagram illustrating a cross section, side views, and top view of anexample 3D multiple qdot quantum structure using local fin depletiontunneling is shown in FIG. 27B. The quantum structure, generallyreferenced 1870, comprises substrate 1879, optional oxide layer 1871,wells 1872, 1876, fin 1873, gate oxide 1877, and overlapping controlgates 1874, 1875. Note that the dotted line indicates the optional oxidelayer that isolates the 3D quantum structure from the substrate. Thesubstrate may comprise standard resistivity, high resistivity, orisolating substrates. The quantum structure 1870 is useful when quantumtransport is needed, i.e. quantum shift and particle spatialentanglement, and can be realized in bulk 3D semiconductor processes,e.g., FinFET, or in SOI 3D semiconductor processes.

A diagram illustrating two example double V fin-gate-fin structureshaving two wells placed in close proximity allowing quantum particles tointeract is shown in FIG. 28A. The quantum interaction gate, generallyreferenced 1880, comprises two 3D structures comprising a plurality ofqdots 1882, 1888, fins 1884, control gates 1886, and interaction qdots1881.

In this embodiment, the inner two semiconductor wells 1881 come in veryclose proximity thereby allowing a strong interaction between particlesor distributed particles in the two qdots. The distance between otherpairs of qdots is significantly larger and thus the interaction betweencorresponding particles is much smaller, ideally negligible. In thismanner, the double V quantum structure shifts two or more particles intospecific positions for a well controlled interaction and then transportsthem apart. The preparation of the quantum state also happens whenparticles are further away and thus can be done largely independent onefrom the other. This also allows a well-controlled interaction betweenparticles only when they are in specific qdots and when the controlsignals are configured to enable the interaction.

A diagram illustrating an example 3D semiconductor quantum structureusing fin-to-fin tunneling through a local depleted region with a sharedwell between two fin paths providing bifurcation is shown in FIG. 28B.The quantum structure, generally referenced 1890, comprises a pluralityof qdots 1892, namely qdots #1, #2, #3, #4, fins 1896, and control gates1894. The well of qdot #2 1898 overlaps two fins to provide pathbifurcation whereby particles can move between qdots #1 and #4 andbetween qdots #3 and #4.

Note that this quantum structure can realize either a bifurcation of thequantum operation path or a merger of the quantum operation path. Thisstructure is useful in creating more complex quantum structures. Notealso that the control gates overlapping the two fins and separatingqdots #1 and #3 can be separated (as shown) or can be shared (notshown).

A diagram illustrating an example quantum structure with dummy gates andgate cuts that separate control and dummy gates is shown in FIG. 28C.The quantum structure, generally referenced 1900, comprises qdots 1902,namely qdots #1 to #6, fins 1904, control gates 1901, contacts 1903,dummy gates 1906 not used in operation of the circuit, and gate cuts1908. Depending on the actual 3D semiconductor process used, dummy gatesmay be needed but they remain floating with no potential. The gates needto be equally spaced and on the edges of the well. In addition, they mayneed to be cut in order to prevent unwanted interactions. The cuttingmay be done on top of a dummy fin, or alternatively without the fin.Although 12 control gates are shown, only four are active.

A diagram illustrating an example hybrid planar and 3D semiconductorquantum structure using both fin-to-fin and well-to-well tunnelingthrough local depletion region is shown in FIG. 28D. The quantumstructure, generally referenced 1910, comprises 3D qdots 1912, fins withportions 1914, 1913, 3D control gate 1918, planar qdots 1911, and planarcontrol gate 1916. This hybrid embodiment uses both 3D and planartunneling structures which is possible in a 3D semiconductor process.The inner quantum structure is planar with two overlapping wells (i.e.qdots) and uses well-to-well tunneling through a local depletion region.The outer, i.e. left and right, quantum structures are 3D and usefin-to-fin tunneling through a local depletion region. Note that the twotypes of tunneling have different barrier levels and thus requiredifferent control gate signals.

The present invention also provides a semiconductor quantum structurethat uses a 3D semiconductor process used to fabricate two semiconductorfins and an overlapping imposing control gate that constitutes thetunneling path from one semiconductor qdot to the other. The tunnelingis controlled by the control gate that imposes the potential on thetunneling path. By modulating the potential of the imposer gate, acontrolled fin-gate and gate-fin tunneling through the thin oxide underthe control gate is enabled, realizing the function of a position/chargequbit. More complex structures with higher number of qdots percontinuous well and larger number of wells can be built. Both planar and3D semiconductor processes can be used to build well/fin-to-gate andgate-to-fin/well tunneling quantum structures. Hybrid 3D and planarstructures can be built as well. By combining a number of suchelementary quantum structures a quantum computing machine is realized.

A diagram illustrating an example 3D semiconductor quantum structureusing fin-to-gate tunneling through oxide is shown in FIG. 29. Thequantum structure, generally referenced 1920, comprises two wells 1921,1927 with fin structures 1923, 1926 to realize the quantum dots #1 and#2, a gate layer with oxide 1924 overlaps both fins and creates atunneling path from one fin to the other. A diagram illustrating a threedimensional view of an example 3D semiconductor quantum structure usingfin-to-gate and gate-to-fin tunneling through oxide is shown in FIG. 30.The quantum structure, generally referenced 1930, comprises fins 1932,1938, overlapping control gate with oxide layer 1936, substrate 1931,and local depletion region 1934. Note that the well may be omitted andthe qdot realized by the semiconductor fin area only.

With reference to FIGS. 29 and 30, the tunneling is controlled by thecontrol terminal that imposes the potential on the tunneling gate. Inone embodiment, the control gate is substantially floating but it iselectrostatically coupled to the control terminal nearby (not shown). Ifthe tunnel barrier is high, the quantum particle is locked in its priorstate. When the control terminal determines a lowering of the barrier,the quantum particle is allowed to tunnel from one qdot to the other.Depending on the pulse width of the control signal, the quantum particleeither completely or partially tunnels through. In the latter case, thequantum particle is distributed between two qdots to achieve a spatialsuperposition state. A thin oxide layer separates the semiconductor finfrom the control gate. Note that in real implementations, the quantumstructure generally has a deformed complex 3D shape where the depletionregion depends on the particular implementation and semiconductorprocess used. The structures shown herein are for illustration purposesonly.

A diagram illustrating a cross section, side view, and top view of anexample 3D semiconductor quantum structure using fin-to-gate tunnelingthrough oxide is shown in FIG. 31. The quantum structure, generallyreferenced 1950, comprises substrate 1951, optional oxide layer 1957,wells 1952, fins 1953, 1955, gate oxide 1956, and overlapping controlgate 1954. Note that the dotted line indicates the optional oxide layerthat isolates the 3D quantum structure from the substrate, i.e. SOIprocess. The substrate may comprise standard resistivity, highresistivity, or isolating substrates.

The tunneling through the oxide in the quantum structure is induced in afin by the overlapping control gate. When the barrier is high, virtuallyno tunneling current is allowed. When the barrier is lowered, tunnelingthrough the gate oxide allows the particle to move from one qdot to theother. If the particle has not completed the move from one qdot to theother, it will spread (equally or non-equally) between two qdots toachieve a superposition state.

A diagram illustrating a cross section of an example 3D semiconductorquantum structure using fin-to-gate and gate-to-fin tunneling is shownin FIG. 32. The quantum structure, generally referenced 1940, comprisessubstrate 1941, optional oxide layer 1942, fins 1945, 1946, gate oxide1944, and overlapping control gate 1943. As described supra, thetunneling through the oxide layer 1944 is controlled by the overlappingcontrol terminal that imposes the potential on the control gate. If thetunnel barrier is high, the quantum particle is locked in its priorstate. When the control terminal determines a lowering of the barrier,the quantum particle is allowed to tunnel from one qdot to the other.

A diagram illustrating a top view of an example two qdot 3Dsemiconductor quantum structure using fin-to-gate tunneling throughoxide is shown in FIG. 33. The quantum structure, generally referenced1990, comprises two wells 1992, 1996 with fin structures 1993 thatrealize quantum dots #1 and #2 and a control gate layer with oxide 1994overlapping both fins creating a tunneling path 1995 for particle 1992from one fin to the other.

Note that different shapes can be used for the layers used to constructthe quantum structure, e.g., squares, rectangles, polygons, circles,composed shapes, etc. as described supra. In this embodiment, two wellsare added, one to each fin which crosses the well in the middle. Whenthe control terminal lowers the barrier, the quantum particle in theleft qdot tunnels to the right qdot.

A diagram illustrating an example double V quantum interaction structureusing 3D semiconductor process with fin-to-gate tunneling is shown inFIG. 34A. The quantum interaction gate, generally referenced 1960,comprises two 3D structures comprising a plurality of qdots 1964, fins1968, control gates 1966, and interaction qdots 1962.

In this embodiment, the inner two semiconductor wells 1962 come in veryclose proximity thereby allowing a strong interaction between particlesor distributed particles in the two qdots. The distance between otherpairs of qdots is significantly larger and thus the interaction betweencorresponding particles is much smaller, ideally negligible. In thismanner, the double V quantum structure shifts two or more particles intospecific positions for a well controlled interaction and them transportsthem apart. The preparation of the quantum state also happens whenparticles are further away and thus can be done largely independent onefrom the other. This also allows a well controlled interaction betweenparticles only when they are in specific qdots and when the controlsignals are configured to enable the interaction.

A diagram illustrating an example quantum structure with fin-to-gatetunneling with dummy gates and cuts to create dummy fins is shown inFIG. 34B. The quantum structure, generally referenced 1970, comprises aplurality of qdots 1972, fins 1973, control gates 1974, contacts 1975,dummy gates 1971 not used in operation of the circuit, and gate cuts1976. Depending on the actual 3D semiconductor process used, dummy gatesmay be needed which remain floating with no potential. The gates need tobe equally spaced and on the edges of the well. In addition, they mayneed to be cut in order to prevent unwanted interactions. The cuttingmay be done on top of a dummy fin, or alternatively without the fin.

A diagram illustrating an example hybrid planar and 3D semiconductorquantum structure using both fin-to-gate and well-to-gate tunneling isshown in FIG. 34C. The quantum structure, generally referenced 1980,comprises 3D qdots 1982, fins 1984, 1986, 3D control gate 1986, planarqdots 1988, and planar control gate 1989. This hybrid embodiment usesboth 3D and planar tunneling structures which is possible in a 3Dsemiconductor process. The inner quantum structure is planar with twowells (i.e. qdots) and uses well-to-gate tunneling through oxide. Theouter, i.e. left and right, quantum structures are 3D and use fin-to-fintunneling through oxide. Note that the two types of tunneling havedifferent barrier levels and thus require different control gatesignals.

A diagram illustrating an example initialization configuration for aquantum interaction structure using tunneling through gate-well oxidelayer is shown in FIG. 35. The circuit comprises a classic well 1100,single particle (e.g., electron) injector circuit 1102, quantum well1104, and control gate 1108. The circuit is operative to separate aquantum behaving electron from the sea of electrons present on thesurrounding classic semiconductor structures, such as well 1100. Thesingle electron injection circuit 1102 takes only one electron from theclassic well situated on its left side and injects it into the quantumwell when the proper control signal is applied. In general, there areseveral ways to control the quantum structure: (1) using electricsignals only, (2) using magnetic signals only, or (3) using acombination of electric and magnetic signals. The electric controlsignal preferably has specified amplitude levels (Vlow/Vhigh) and givenpulse width. The magnetic control signal is preferably of appropriatestrength.

Note that the magnetic field control can be used to select an electronwith a given spin orientation. This uses the property of electrons toorient their spin depending on the direction of the magnetic fielddirection at the time when the single electron was isolated from theclassic sea of electrons. The direction of the magnetic field can bechanged and thus the two spin orientations can be individually selected.

In order to perform a quantum operation in a given quantum structurehaving two or more qdots, the quantum system first needs to beinitialized into a known base state. One or more electrons can beinjected into the multi-qdot quantum structure. These single electronsare injected only into some of the qdots of the overall quantumstructure. Next, control imposing signals are applied that determine thequantum evolution of the state and perform a certain desired quantumoperation.

In general, the quantum operation performed depends on the specificcontrol signals applied. In the case of a single position/charge qubitincluding two qdots that can realize a generalized phase rotation of thequantum state, the rotation angle is dependent on the pulse width of thecontrol signal applied as compared to the Rabi (or occupancy state)oscillation period.

In a two qdot quantum system, if the tunneling barrier is lowered andkept low, a quantum particle starting from one of the qdots will begintunneling to the next qdot. At a given time of half the Rabi oscillationperiod the particle will be completely on the second qdot, after whichit will start tunneling back to the first qdot. At a certain time, theparticle will have returned to the first qdot, after which the processrepeats itself. This process is called the Rabi or occupancy oscillationand its period is named the Rabi or occupancy oscillation period. Thephase rotation in a two qdot system will depend on the control signalpulse width as related to the Rabi oscillation period.

A diagram illustrating an example initialization configuration for aquantum interaction structure using tunneling through a local depletedregion in a continuous well is shown in FIG. 36. The circuit comprises aclassic well 1110, single particle (e.g., electron) injector circuit1112, quantum well 1114, and control gate 1118. The quantum structurecomprises two qdots (additional qdots are possible) on either side ofthe control gate 1118, and a tunneling path (represented by the arrow)that has a partial overlap with the qdots. The quantum operation iscontrolled by a control gate (or control terminal) 1118 situated inclose proximity of the tunneling path.

In one embodiment, the qdots are implemented by semiconductor wells,while the tunneling path is realized by a polysilicon layer thatpartially or completely overlaps the two wells. The tunneling appearsvertically over the thin oxide layer between the semiconductor well andthe polysilicon layer. The control terminal is realized with anotherwell or another polysilicon layer placed in close proximity in order toexercise reasonable control over the tunneling effect.

In another embodiment, a semiconductor quantum processing structure isrealized using lateral tunneling in a local depleted well. The two qdotsare linked by a region that is locally depleted where the tunnelingoccurs (represented by the arrow). The control terminal typicallyoverlaps the tunneling path in order to maintain well-controlleddepletion of the entire linking region between the two qdots. Thisprevents direct electric conduction between the two qdots.

In another embodiment, the two qdots of the quantum structure arerealized by a single semiconductor well having a control polysiliconlayer on top. The tunneling occurs laterally/horizontally through thedepleted region that isolates the two qdots.

It is noted that quantum structures can be implemented in semiconductorprocesses using various tunneling effects. One possible tunneling is thethrough a thin oxide layer. In most semiconductor processes the thinnestoxide is the gate oxide, which can span several atomic layers. In someprocesses, the oxide layer used by the metal-insulator-metal (MIM)capacitance is also very thin. Another example is the tunneling througha depleted region between two semiconductor well regions. Such a localdepleted region may be induced by a control terminal into an otherwisecontinuous drawn well or fin.

A diagram illustrating an example planar semiconductor quantum structureusing tunneling through oxide layer is shown in FIG. 37A. Thesemiconductor qubit, generally referenced 1120, comprises two qdots1124, 1128, partial overlapped polysilicon gate 1129 and vertical thinoxide tunneling 1126, and can contain a particle 1122.

A diagram illustrating an example planar semiconductor quantum structureusing tunneling through local depleted well is shown in FIG. 37B. Thesemiconductor qubit, generally referenced 1130, comprises two qdots1134, 1138, control gate 1139, and horizontal local depleted welltunneling 1136, and can contain a particle 1132.

Note that there are numerous types of semiconductor processes. Some areplanar, while others are used to fabricate 3D structures (e.g., FinFET).A diagram illustrating an example 3D process semiconductor quantumstructure using tunneling through oxide layer is shown in FIG. 37C. Thesemiconductor qubit, generally referenced 1140, comprises two qdots1142, 1143, control gate 1145, 3D fins 1146, 1141, and partialfin-to-gate overlap and vertical thin oxide tunneling 1148, and cancontain a particle 1144.

A diagram illustrating an example 3D process semiconductor quantumstructure using tunneling through local depleted well is shown in FIG.37D. The 3D semiconductor qubit, generally referenced 1150, comprisestwo qdots 1154, 1153, control gate 1155, 3D fins 1156, 1151, andhorizontal local depleted fin tunneling 1158, and can contain a particle1152.

In one embodiment, controlled-NOT (CNOT) quantum gates can be realizedwith any of the above described qubit structures implemented in eitherplanar or 3D semiconductor processes.

A diagram illustrating an example CNOT quantum interaction gate usingtunneling through oxide layer implemented in planar semiconductorprocesses is shown in FIG. 38A. The quantum interaction gate comprisestwo qubits, qubit A and qubit B, with each qubit comprising two qdots1166, 1163, tunneling path 1161, and control terminal 1168. Qdots 1 and2 of qubit A and qdots 3 and 4 of qubit B are arranged such that qdots 2and 3 are close enough for (possibly present there) particles 1164 tointeract, for example, in an electrostatic manner.

A diagram illustrating an example CNOT quantum interaction gate usingtunneling through local depleted well implemented in planarsemiconductor processes is shown in FIG. 38B. The quantum interactiongate comprises two qubits, qubit A and qubit B, with each qubitcomprising two qdots 1186, 1183, tunneling path 1188, and controlterminal 1181. Qdots 1 and 2 of qubit A and qdots 3 and 4 of qubit B arearranged such that qdots 2 and 3 are close enough for particles 1184 tointeract.

A diagram illustrating an example CNOT quantum interaction gate usingtunneling through oxide layer implemented in 3D semiconductor processesis shown in FIG. 38C. The quantum interaction gate comprises two qubits,qubit A and qubit B, with each qubit comprising two qdots 1174, 1177,tunneling path 1171, 1173, 1175, and control terminal 1178. Qdots 1 and2 of qubit A and qdots 3 and 4 of qubit B are arranged such that qdots 2and 3 are close enough for particles (if present there) 1176 tointeract.

A diagram illustrating an example CNOT quantum interaction gate usingtunneling through local depleted fin implemented in 3D semiconductorprocesses is shown in FIG. 38D. The quantum interaction gate comprisestwo qubits, qubit A and qubit B, with each qubit comprising two qdots1192, 1198, tunneling path 1196, and control terminal 1194. Qdots 1 and2 of qubit A and qdots 3 and 4 of qubit B are arranged such that qdots 2and 3 are close enough for particles 1190 to interact.

Quantum Interaction

Quantum computing is based on the interaction between two or moreindividual particles that have been separated from a collectivity andwhich follow the laws of quantum mechanics. In order for two particlesto interact, they generally need to be brought in close proximity.Particles that are relatively far away from one another have a small ornegligible interaction.

Each particle carries information in its position and/or spin.Position/charge qubit based quantum computing uses the position toencode information, while spin qubit based quantum computing uses thespin of the particles to encode information. Hybrid qubits use both theposition and the spin to encode information.

The two or more particles that need to interact and thus make anexchange of information need to be separately initialized in theircorresponding quantum state. The separation may be either in distance,ensuring a negligible interaction of the particles as they areinitialized, or in time when the particles are initialized at differenttime instances. In some embodiments both space and time separation maybe used to ensure isolation between the two or more starting quantumstates.

When two or more quantum particles/states are brought in closeproximity, they interact with one another and in the process exchangeinformation. We call the particles entangled as each of the particlescarry information from all particles that have interacted. After theentanglement has occurred, the particles are moved at large distance andthey still carry the entire information contained initially by thedistinct initialized states. If measurement/detection is perform on oneof the particles from the entangled ensemble, the corresponding quantumstate will be collapsed. By measuring, for example, a charge qubit it isdetermined whether the particle is present or not in a given qdot. Whenone qubit is measured the corresponding component from the other qubitsthat are part of the entangled ensemble will also collapse.

In the case of semiconductor quantum structures based on tunnelingthrough a local depletion region induced in a continuous well under thecontrol of a gate terminal, the tunneling current is the quantum physicseffect that governs the operation of the structure. The tunnelingeffect/current is dependent on one side on the tunnel barrier height,which in turn depends on the signal level applied at the controlterminal. A second element that impacts the tunnel barrier and thus thetunneling effect is the presence of any other particle (one or more) inproximity of the target qubit. The presence or absence of anotherparticle will change the Rabi oscillation frequency of a given targetqubit. In a double qdot system when the control terminal determines alowering of the tunnel barrier, the quantum particle will starttunneling forth and back between the two qdots. The precise position ofthe particle will depend on the pulse width of the control signal thatenables the Rabi oscillation.

In order to get interaction between two particles present in theirrespective qubits, a semiconductor system with at least four qdots isneeded as shown in FIG. 39A. There are multiple ways of operating a twoqubit quantum structure, depending on how and what control signals areapplied. In one embodiment of the quantum interaction gate, one of thetwo qubits may be designated as the “target” qubit and the other as the“control” qubit. The state evolution of the target qubit will beimpacted by the state of the control qubit. The control qubit staysfixed during the interaction and only the target qubit will change itsmeasured state. In the interaction process, however, both particles willentail changes as a result of their entanglement. In the position/chargequbit implementation, the spin of the control qubit may change as aresult of the interaction, while the position of the target qubit willchange as a result of the interaction. Any combination of position andspin changes are possible for the target and control qubits. In thisembodiment, only the target qubit control terminal receives a pulse.Various quantum gates can be constructed in this way, including thecontrolled-NOT quantum gate, the Toffolli (control-control-NOT) quantumgate, the controlled rotation quantum gate, and the ancillary quantumgate.

Moving the quantum particles/states to and from given quantum gates isperformed with quantum shift registers. Their length and orientation arepreferably such that it links the different quantum gates into acorresponding quantum circuit based on a particular quantum algorithm.

In yet another embodiment of the quantum interaction gate, both (or all)qubits are allowed to change in their measured state (position, spin, orboth). To achieve this both (or all) control terminals are pulsed. As aresult, both (or all) particles that enter entanglement will have theirmeasured state changed (position, spin, or both). As a byproduct of theentanglement, the other non-measured dimension may experience changes aswell, e.g., the spin in a position qubit or the position in a spinqubit.

A diagram illustrating a first example controlled NOT double qubitstructure and related Rabi oscillation is shown in FIG. 39A. The topcontrol qubit 1200 comprises two qdots which can contain particle 1202.The lower target qubit 1204 comprises two qdots and can contain particle1206. In one example, the control qubit may have a vertical orientationof its double qdot, while the target qubit may have a horizontalorientation of its double qdot. Other orientation combinations arepossible, including angled or slanted.

In operation, when the particle 1202 of the control qubit is in itsfurther away position we denote this quantum state as |0>. The Rabioscillation frequency 1201 (or period) of the target qubit has a firstvalue. If a control signal 1208 is applied to the target qubit that hasa pulse width equal to the Rabi period, the particle will tunnel forwardand back to its initial position resulting in keeping its originalstate. This is valid for both base quantum states when the particles arenot in split states. For example, if the particle is initially presentin the left qdot of the target qubit (we can arbitrarily denote thisstate as |0>) at the beginning of the control signal pulse, the particlewill be back in the left qdot at the end of the pulse and thus the state|0> is preserved. If the particle was initially in the right qdot of thetarget qubit (we denote that state as |1>) as shown in FIG. 39B, thestate is again preserved at the end of the control pulse equal to theRabi period 1210 when the control particle is further away.

Now if the particle of the control qubit is moved to the closer-inposition (which we denote by the quantum state |1>), as shown in FIG.39C, the Rabi oscillation frequency and period will be modified as aresult of the interaction between the two particles. In one example, theRabi oscillation frequency of the target qubit is decreased as comparedto dashed curve 1214 and its corresponding Rabi oscillation period 1212is increased. If the same control pulse width is applied as before, theparticle no longer has enough time to tunnel forward and back to itsinitial position. In this case the pulse width of the control signal isjust enough for the particle to tunnel from the left qdot to the rightqdot. This corresponds to an inversion or a NOT operation.

In FIG. 39C the particle that was initially in the left qdot (state |0>)has time to fully go to the right qdot (state |1>) with Rabi oscillationperiod 1212. In FIG. 39D the particle that was initially in the rightqdot (state |1>) has time to fully go to the left qdot (state |0>) withRabi oscillation period 1216. This corresponds to a controlled quantuminversion operation, hence the name controlled-NOT.

In the controlled-NOT quantum operation, the inversion applies not onlyto the base states |0> results in |1> and |1> results in |0>, but alsoapplies to any superposition of quantum state a|0>+b|1> which goes tob|0>+a|0>. Such an operation 1222 for the quantum gate 1220 is shown inFIG. 40. The CNOT operation for full particle inversion is shown on thetop right for two base state qubits. Both target and control qubits arein base states/full particle operation. In the state 1224 beforeinversion, the particles of both control and target qubits are in leftpositions. In the state 1226 after invention, the particle of the targetqubit is in the right position.

In the middle is illustrated the CNOT operation for split particleinversion. In the state 1228 before inversion, the control qubit is in abase state, while the target qubit is in a split state. In the state1230 after inversion, the target qubit state is inverted.

In the bottom is illustrated the CNOT operation for superpositioninversion. In the state 1232 before inversion, both the control and thetarget qubits are in split states. In the state 1234 after inversion,the target qubit state is inverted. This is the more general quantumCNOT operation case.

Note that the controlled-NOT quantum gate together with the Hadamardgate form a fundamental quantum set, which means that any quantumalgorithm can be built with a given combination of these two fundamentalquantum gates.

To precisely obtain the functionality of a quantum CNOT, the distancebetween the four qdots is preferably such that when the controlqubit/particle changes its position from the |0> to the |1> base state,the corresponding Rabi oscillation period of the target qubit is doubled(i.e. the frequency is halved). The control signal of the target qubitis also preferably equal to the Rabi period in the state |0> of thecontrol qubit.

If these conditions are not satisfied, the quantum interaction gate willnot have a CNOT operation, but a different controlled rotationoperation. In this case, the two particles still interact and thecorresponding Rabi oscillation period is changed, but not to a doublevalue for the CNOT operation, but to some other value that results in adifferent particle splitting/rotation.

In real life implementations of such semiconductor quantumgates/structures, there are process variations (e.g., distances,thicknesses, dimensions, etc.) and also variability of the controlsignals (e.g., pulse width variabilities) which result in differentamounts of Rabi oscillation period modifications. In one embodiment, acalibration procedure of the semiconductor quantum gate is applied toachieve CNOT functionality. An advantage of the semiconductor quantumimplementation is that the integrated circuits approach allows theindividual calibration of each quantum gate in the system. Thiscompensates both for the random and the deterministic components of thevariability.

A diagram illustrating an example controlled NOT quantum interactiongate using square layers with partial overlap and tunneling throughoxide layer is shown in FIG. 41A. The CNOT quantum interaction gate,generally referenced 1360, comprises imposers 1362, 1364 each withseparate control pulses, PULSE A and PULSE B, control gates 1363, andqdots 1361. Particles 1366, 1368 interact to provide the CNOTfunctionality. Note that only two chain paths have been used in thiscase. It is appreciated that other shapes, e.g., rectangle, etc., may beused.

A diagram illustrating an example Toffoli quantum interaction gate usingsquare layers with partial overlap is shown in FIG. 41B. Thecontrolled-controlled NOT (CCNOT) quantum interaction gate (or Toffoligate), generally referenced 1370, comprises imposers 1372, 1374, 1376each with separate control pulses, control gates 1379, and qdots 1375.Particles 1378, 1371, 1373 interact to provide the CCNOT functionality.It is appreciated that other shapes, e.g., rectangle, etc., may be used.

A diagram illustrating an example higher order controlled NOT quantuminteraction gate using square layers with partial overlap is shown inFIG. 41C. In a similar manner, higher order quantum interaction gatescan be constructed. The semiconductor n^(th) order CNOT (n-CNOT) usingsquare layers with partial overlap, generally referenced 1380, comprisesa plurality of qdots 1386 making up multiple qubits, imposers 1382,control gates 1387, and particles 1384. It is appreciated that othershapes, e.g., rectangle, etc., may be used.

A diagram illustrating a first example of semiconductor entanglementquantum interaction gate including initialization, staging, interaction,and output locations is shown in FIG. 42A. The quantum interaction gate,generally referenced 1240, in the shape of double V comprises two qubitsin close proximity and gradual increasing of the distance between thestaging and initialization/detection or output locations to minimizeparasitic interaction. Other shapes are also possible, while achievinglarge distance when interaction is not desired and close distance wheninteraction is desired. Interaction occurs between the two interactionqdots 1243, 1244.

A diagram illustrating a second example of semiconductor entanglementquantum interaction gate including initialization, staging, interaction,and output locations is shown in FIG. 42B. The quantum interaction gate,generally referenced 1250, in the shape of T comprises two qubits inclose proximity and gradual increasing of the distance between thestaging and initialization/detection or output locations to minimizeparasitic interaction. Other shapes are also possible, while achievinglarge distance when interaction is not desired and close distance wheninteraction is desired. Interaction occurs between the two interactionqdots.

A diagram illustrating a third example of semiconductor entanglementquantum interaction gate including initialization, staging, interaction,and output locations is shown in FIG. 42C. The quantum interaction gate,generally referenced 1260, comprises two qubits whose interaction qdotsare situated in close proximity and gradual increasing the distancebetween the staging and initialization/detection or output locations tominimize parasitic interaction. In this case, the particles are shiftedforward and back through the same qdots. This structure is called theI-interaction structure. It has the same main characteristics as thedouble-V structure, but particles are traveling through the same qdotsforward and back, instead of different loading (move-in) and de-loading(move-out) paths, like in FIG. 42A.

A diagram illustrating a fourth example of semiconductor entanglementquantum interaction gate including initialization, staging, interaction,and output locations is shown in FIG. 42D. The quantum interaction gate,generally referenced 1270, in the shape of H comprises three qubitsforming main paths 1 and 2, and interactor path 3, in close proximitywith gradual increasing of the distance between the staging andinitialization/detection or output locations to minimize parasiticinteraction. Other shapes are also possible, while achieving largedistance when interaction is not desired and close distance wheninteraction is desired. First and second interaction occurs between thetwo pairs of interaction qdots.

In a quantum core, a large number of interactions between the differentquantum states/particles needed to be performed. Using the double-V andmultiple-V quantum interaction structures a quantum core with relativelyparallel quantum paths can be realized.

A diagram illustrating an example quantum interaction gate using doubleV interaction between neighboring paths is shown in FIG. 43A. Thequantum interaction gate, generally referenced 1280, comprises close-byinteraction qdots and further-away qdots for negligible parasiticinteraction, input quantum state 1281, output quantum 1282, a pluralityof N quantum paths 1283, and double V interaction 1284 between pathswhere the interactions are allowed between neighboring quantum paths.

A diagram illustrating an example quantum interaction gate using Hinteraction between neighboring paths is shown in FIG. 43B. The quantuminteraction gate, generally referenced 1290, comprises close-byinteraction qdots and further-away qdots for negligible parasiticinteraction, input quantum state 1291, output quantum state 1292, aplurality of N quantum paths 1293, and H shaped interaction 1294 betweenpaths where the interactions are allowed between neighboring quantumpaths.

In some cases, it may be desirable to perform interactions not onlybetween neighboring paths or qdots. A diagram illustrating an examplequantum interaction ring with star shaped access and double Vinteraction with multiple next door neighbors (with multiple detectionpoints) is shown in FIG. 43C. The quantum interaction ring (or hub),generally referenced 1300, comprises interaction ring 1304, inputquantum state 1302, a plurality of double V interactions 1306, and aplurality of detectors 1301. Any of the quantum states in the spokes ofthe ring configuration can be moved into the ring to interact withanother quantum state.

A diagram illustrating an example quantum interaction ring with starshaped access and H interaction with multiple next door neighbors isshown in FIG. 43D. The quantum interaction ring, generally referenced1310, comprises interaction ring 1316, input quantum state 1314, aplurality of H shaped interactions 1318, and plurality of detectors1312. Any of the quantum states available in the star configuration canbe brought to the ring to interact with another state.

Numerous shapes can be used to implement CNOT quantum interaction gates.A diagram illustrating an example T shape quantum interaction gate usingtunneling through a local depleted well for interaction between twoqubits is shown in FIG. 44A. The quantum interaction gate, generallyreferenced 1320, comprises two qubit paths labeled 1 and 2. The CNOTgate allows interaction between two particles implemented usingstructures with tunneling 1325 through a local depleted well and T-shapechains. The qubits comprise a plurality of qdots 1323, 1326, and controlgate 1324. A four qdot interaction structure 1321 shows the possibleinteraction between the two qubits. An alternative four qdot interactionstructure 1322 is also possible. Alternatively, the T shape CNOT quantuminteraction gate, generally referenced 1327, can be constructed withpaths 1 and 2, where path 2 is L shaped.

A diagram illustrating an example H shape quantum interaction gate usingtunneling through a local depleted well for interaction between threequbits is shown in FIG. 44B. The quantum interaction gate, generallyreferenced 1330, comprises three qubits paths, namely 1, 2, and 3 whichinclude quantum shift registers. Each qubit comprises a plurality ofqdots 1335, 1338, control gate 1336, and tunneling through a localdepleted well 1337. Note that other shapes such as I-shape, T-shape,L-shape can also be realized. Both orthogonal (i.e. vertical andhorizontal) and angled structures can be used. Several possible qdotinteraction structures are possible including four qdot interactionstructures 1331, 1332, 1333, 1334.

A diagram illustrating an example of a triple V shape quantuminteraction gate is shown in FIG. 44C. The quantum interaction gate,generally referenced 1340, comprises a plurality of qdots 1341, 1343,control gates 1344, and tunneling through a local depleted well 1342 forinteraction between three qubit paths or qudits (paths 1, 2, and 3). Thetriple-V interaction structure allows the entanglement of threeparticles using two consecutive two-particle entanglement.

Note that if more than two particles need to interact, it is not neededto bring them simultaneously in close proximity. Multiple V-paths can beused to bring together pairs of particles/states to interact. In somecases, it is desired to achieve interaction/entanglement betweenmultiple particles/states. A triple-V quantum structure (or in general amulti-V structure) can be used to achieve this. There are twointeraction locations: (1) between the first and second V-shape quantumstructure, and (2) between the second and the third V-shape quantumstructure. In this case, an even larger number of quantum shiftregisters are used to transport the quantum particles/states between,to, and from the interaction locations.

Another example of interaction shape is X or star-shape. A diagramillustrating an example double V shape quantum interaction gate usingtunneling through a local depleted well for interaction between twoqubits is shown in FIG. 44D. The X shaped quantum interaction gate,generally referenced 1350, comprises a plurality of qdots 1351, 1354,control gates 1352, and local depleted well 1353. The X-interactionstructure allows entanglement of four particles, either simultaneouslyor at consecutive times), where each well has bidirectional particletransport. Note that the X-shape (or star-shape) is a version ofdouble-V quantum interaction in which the two V-shapes are split in themiddle. This allows the interaction between a larger number ofparticles.

One of the most efficient ways to build a quantum core is using a gridconfiguration in which the qdots are arranged in rows and columns. Adiagram illustrating a first example CNOT quantum interaction gatewithin a grid array of programmable semiconductor qubits is shown inFIG. 45A. The re-configurable grid-based quantum computing structure,generally referenced 1360, comprises a plurality of qubits 1362 arrangedin rows and columns and associated control circuitry including controlsignals generator 1364. As an example, a double-V interaction structureis shown programmed as indicated by the four arrows. Note that the gridarray of qubits can be re-programmed to implement other structures andconfigurations.

A diagram illustrating a second example CNOT quantum interaction gatewithin a grid array of programmable semiconductor qubits is shown inFIG. 45B. The re-configurable grid-based quantum computing structure,generally referenced 1370, comprises a plurality of qubits 1372 arrangedin rows and columns and associated control circuitry including controlsignals generator 1374. As an example, a double-V interaction structureis shown programmed as indicated by the four arrows. Note that the gridarray of qubits can be re-programmed to implement other structures andconfigurations.

Most of the structures described supra use charge qubits and qdots thatare electrically controlled via an electric field. A more generalquantum structure can use hybrid electric and magnetic control. Themagnetic field can be generated with an inductor or a resonator. Adiagram illustrating an example quantum interaction gate constructedwith both electric and magnetic control is shown in FIG. 46. Thestructure, generally referenced 1380, comprises a quantum interactiongate located within a magnetic control 1384, and electric control 1382.In this example, the hybrid electric and magnetic control is applied toa double-V structure using tunneling through local depleted regions. Oneor more gates can be under the control of a magnetic field generationstructure. In one embodiment, given a focused magnetic field, thecontrol is local if only one interaction structure is covered by thestrong magnetic field from the inductor (or resonator). Note that thesize and shape of the magnetic field generator can vary.

In the case of a larger quantum core, multiple inductors can be used tocreate local magnetic control fields. Alternatively, a global magneticcontrol can be used, which impacts two or more quantum structures at atime. A diagram illustrating an example grid array of programmablesemiconductor qubits with both global and local magnetic is shown inFIG. 47. The structure, generally referenced 1390, comprises a pluralityof qubits 1398 arranged in rows and columns, a plurality of localmagnetic controls 1396 (per quantum gate), a global magnetic control1392, and an electric control 1394. With global magnetic control,multiple quantum structures are controlled by the same magnetic field.One example use for the magnetic field is to select the spin orientationof the particles that are loaded in the quantum structures/core.

First through eighth stages of an example quantum interaction gateparticle interaction are shown in FIGS. 48A through 48H, respectively.FIG. 48A illustrates the initializing of an H-style quantum interactiongate with injecting particles 1400, 1402, 1404. All particles can beinjected at the same time. In this case, however, some particles maystay in qdots for long time intervals before they undergo processing.This results in loss of quantum accuracy due to decoherence. It is thusadvantageous to load the particles only as they are needed in thequantum computation flow. In FIG. 48B, the splitting of particle into1406 and 1408, and spatial entanglement are shown.

Once the particles are injected, they can be split as shown in FIG. 48Cand transported to the interaction qdots. In the H-style interactor, theinteractor particle 1410 is moved around to realize the desiredinteractions. The interactor particle is split 1414 and the interaction1412 between the first path and the interactor path occurs as shown inFIG. 48D. FIG. 48E illustrates the transport of the interactor particle1416 towards the second main path on the right side of the H structure.FIG. 48F illustrates the transporting of the particle 1418 in the secondmain path towards the interaction position.

FIG. 48G illustrates the performing of the second interaction 1420 ofthe split particle 1422 between the second main path and the interactorpath. In this manner, the first main path interacts with the second mainpath via the interactor. Subsequently, the states are shifted away fromthe interacting position towards the output qdots 1424, 1426 wheredetectors are located. FIG. 48H illustrates the detecting process andthus the collapsing of the quantum states.

A diagram illustrating an example semiconductor double qdot qubit usingtunneling through a separate layer planar structure is shown in FIG.49A. The planar semiconductor qubit, generally referenced 1430, usesthin gate oxide tunneling and comprises qdots 1434, 1438, control gate1432, and polysilicon or oxide 1436.

A diagram illustrating an example planar semiconductor double qdot qubitusing tunneling through a local depleted well planar structure is shownin FIG. 49B. The planar semiconductor qubit, generally referenced 1440,uses tunneling 1448 through a local depletion region inside a continuouswell, and comprises qdots 1444, 1441, control gate 1446, and contact1442.

A diagram illustrating an example 3D semiconductor qubit using tunnelingthrough a separate gate oxide layer 3D FIN-FET structure is shown inFIG. 49C. The 3D semiconductor qubit with fin-to gate tunneling 1471,generally referenced 1450, comprises qdots 1454, 1456, fins 1458, andcontrol gate 1452.

A diagram illustrating an example 3D semiconductor qubit using tunnelingthrough a local depletion in a fin structure is shown in FIG. 49D. The3D semiconductor qubit with local depleted fin tunneling 1473, generallyreferenced 1451, comprises qdots 1453, 1455, fins 1459, and control gate1457.

A diagram illustrating a semiconductor CNOT quantum interaction gateusing two qubit double qdot structures with tunneling through a separateplanar structure is shown in FIG. 49E. The CNOT quantum interactiongate, generally referenced 1460, comprises a first qubit having aplurality of qdots 1466, control gate 1464, and metal layer 1462 abovethe control gate 1464. A second qubit comprises a plurality of qdots1465, control gate 1463, and contact 1467. The two qubits are located inclose proximity so that interaction occurs between qdots 1468 and 1461.Other interactions may occur as indicated by the arrows but these aremuch weaker since the qdots are further away from each other.

Semiconductor CNOT gates can be built using tunneling through adepletion region. Several different positions for getting interactionbetween two or more particles inside the same continuously drawn wellwill now be described. In this case, the two interacting particles arenot on separate chain structures, but inside the same chain structure.

A diagram illustrating a first example quantum interaction gate withinteraction between two particles in the same continuous well is shownin FIG. 49F. The quantum interaction gate, generally referenced 1470,comprises a plurality of qdots in the same continuous well, twoparticles 1476, 1478, and control gates 1472, 1474. Since the twoparticles are separated by the top qdot, the interaction in this exampleis weaker.

A diagram illustrating a second example quantum interaction gate withinteraction between two particles in the same continuous well is shownin FIG. 49G. The quantum interaction gate, generally referenced 1480,comprises a plurality of qdots in the same continuous well, twoparticles 1486, 1488, and control gates 1482, 1484. Since the twoparticles are in adjacent qdots, the interaction in this example isstronger.

A diagram illustrating a third example quantum interaction gate withinteraction between two particles in the same continuous well is shownin FIG. 49H. The quantum interaction gate, generally referenced 1490,comprises a plurality of qdots in the same continuous well 1491, twoparticles 1496, 1498, and control gates 1494. Since the two particlesare in adjacent parallel qdots, the interaction in this example is thestrongest.

In an alternate embodiment the two particles that will interact can behosted by two different chain structures. A diagram illustrating a firstexample quantum interaction gate with interaction between two or moreparticles in different continuously drawn wells is shown in FIG. 49I.The quantum interaction gate, generally referenced 1500, comprises twoqubits with shared control gates 1502, and two particles 1506, 1508. Thequbits are located in close proximity to permit strong interactionbetween the particles.

A diagram illustrating a second example quantum interaction gate withinteraction between two particles in different continuous wells is shownin FIG. 49J. The quantum interaction gate, generally referenced 1510,comprises two qubits with separate control gates 1512, 1514 and twoparticles 1516, 1518. The qubits are not located in close proximity thusresulting in a weaker interaction between the particles.

A diagram illustrating a second example quantum interaction gate withinteraction between two particles in different continuous wells is shownin FIG. 49K. The quantum interaction gate, generally referenced 1520,comprises two qubits with shared control gates 1522, 1524 and twoparticles 1526, 1528. Although the qubits are located in closeproximity, the particles are not in adjacent qdots thus resulting in aweaker interaction between the particles.

A diagram illustrating a second example quantum interaction gate withinteraction between two particles in different continuous wells is shownin FIG. 49L. The quantum interaction gate, generally referenced 1530,comprises two qubits each with separate control gates 1532, 1534, andtwo particles 1536, 1538. Although the qubits are located at thepinnacle of their respective V structures, the two qubits are skewedfrom each other thus resulting in weaker interaction between theparticles.

Note that to get the full operation of the CNOT quantum interactiongate, the gate needs to be initialized and at the end measured.Additional layers are needed to perform such operations. The gate may beoperated by itself (interconnect directly to the classic world), or itmay be interconnected with other quantum gates. A diagram illustrating aCNOT quantum interaction gate using two qubit double qdot structureswith tunneling through a separate oxide layer (partial overlapped gate)implemented in a planar process with gating to classic circuits is shownin FIG. 50A. In particular, the gating to the classic electroniccircuits is shown including reset, injection, imposing, and detection.The imposers use indirect floating potential imposing. The CNOT quantuminteraction gate, generally referenced 1540, comprises two qubits spacedin close proximity to each other such that qdots 1548 and 1541 caninteract electrostatically. The first qubit comprises qdot 1546, gate1542, floating gate 1544 and interface 1549 to classic (i.e.non-quantum) circuitry. The second qubit comprises gate 1545, floatinggate 1543, qdot 1547, and an interface to classic circuitry.

A diagram illustrating a CNOT quantum interaction gate with tunnelingthrough a local depleted well using voltage driven gate imposing andgating to classic circuits is shown in FIG. 50B. The CNOT quantuminteraction gate, generally referenced 1550, comprises two qubits eachhaving a continuous well divided into two qdots 1553, 1557, depletionregion 1563, two gates 1554, 1555, contacts 1552, 1558, 1562, andinterface device 1556, 1560 to classic circuitry. The CNOT semiconductorquantum interaction gate uses direct voltage potential imposing. It hastunneling through a local depleted well using voltage driven gateimposing. It also features gating to classic electronic circuits.

A diagram illustrating a CNOT semiconductor quantum interaction gatewith tunneling through a local depleted well using voltage driven gateimposing and multiple gating to classic circuits is shown in FIG. 50C.The CNOT quantum interaction gate, generally referenced 1570, comprisestwo qubits with tunneling through a local depleted well using voltagedriven gate imposing, having multiple gates towards the classicelectronic circuits. Each qubit comprises continuous well 1578 dividedinto three qdots, a plurality of imposer control gates 1574 withcontacts 1572, depletion region 1573, and interface 1576 to classiccircuitry. The qubits are located in close proximity to permitinteraction between particles. It has more Qdots separated by imposergates that overlap the linear section of the well.

A diagram illustrating an example quantum interaction gate withcontinuous well incorporating reset, inject, impose, and detectcircuitry is shown in FIG. 50D. The quantum interaction gate, generallyreferenced 1590, comprises a continuous well 1598 with a plurality ofcontrol gates 1599, 1601, depletion regions 1600, interfaces 1596, 1602to classic circuitry, reset circuit 1591, injector circuit 1592,imposer(s) circuits 1593, and detector circuit 1594. In this case, theimposers that isolate the adjacent qdots overlap the folded side of thecontinuous well.

A diagram illustrating an example double V CNOT quantum interaction gateusing separate control gates that mandates larger spacing resulting in aweaker interaction is shown in FIG. 51A. In this structure, no commongates are used thus the distance between the two wells that host the twoparticles that will interact are forced to be at a larger distance fromeach other. The quantum interaction gate, generally referenced 1610,comprises two qubits arranged in a double V configuration. Each qubitcomprising a continuous well 1613 divided into a plurality of qdots bycontrol gates 1612 having contacts 1611, interface 1618 to classiccircuitry, and interaction qdot 1614. The two qubits use tunnelingthrough local depleted well and separate control gates that result inlarger spacing and further away placement resulting in a weakerinteraction.

A diagram illustrating an example double V CNOT quantum interaction gateusing common control gates for sections in closer proximity to permitsmaller spacing and stronger interaction is shown in FIG. 51B. Thequantum interaction gate, generally referenced 1620, comprises twoqubits arranged in a double V configuration. Each qubit comprising acontinuous well 1621 divided into a plurality of qdots by common controlgates 1623 having contacts 1624 and separate control gates 1626 havingcontacts 1627, interface 1622 to classic circuitry, and interaction qdot1625. The two qubits use tunneling through local depleted well andshared control gates that result in closer placement and thus strongerinteraction.

The entanglement of the particles depends strongly on the distance thetwo or more particles are brought together. The closer the particlesare, the higher the level of interaction between them. A diagramillustrating an example double V CNOT quantum interaction gate usingcommon control gates for two control gates on both sides of theinteracting qdots is shown in FIG. 51C. The double-V CNOT uses commoncontrol gates for the sections that are in closer proximity in order toallow a smaller spacing and thus a stronger interaction. To be able tobring the two wells at the minimum distance allowed by the process, allgates adjacent to the wells that are at the minimum distance are shared.This is because the gate-to-gate spacing is increasing the well-to-wellminimum separation. The gates that are further away can be separate.

The larger the number of common gates between the two or more wells, themore constraints exist in the operation of the quantum gate (i.e. theparticles are not moving independently but their move is correlated dueto the common gate control). The quantum interaction gate, generallyreferenced 1640, comprises two qubits arranged in a double Vconfiguration. Each qubit comprising a continuous well 1641 divided intoa plurality of qdots by common control gates 1643 having contacts 1645and separate control gates 1644 having contacts 1647, interface 1642 toclassic circuitry, and interaction qdot 1646. This structure uses commoncontrol gates only for the two control gates on both sides of the qdotsthat are interacting. These two gates are the most important since theyset the minimum spacing between the wells. The two qubits use tunnelingthrough local depleted wells and common control gates that result in theclosest placement for strong interaction. This restricts the operationsomewhat, but allows for a much stronger interaction, due to the closerposition of the interaction qdots.

A diagram illustrating an example double V CNOT quantum interaction gateincorporating inject, impose, and detect circuitry is shown in FIG. 51D.The quantum interaction gate, generally referenced 1660, comprises twoqubits arranged in a double V configuration. Each qubit comprising acontinuous well 1664 divided into a plurality of qdots by separatecontrol gates 1666 having contacts, interface 1668 to classic circuitry,imposer circuit 1661, injector circuit 1662, detector circuit 1663, andinteraction qdot 1665. The two qubits are skewed and use tunnelingthrough local depleted well and separate control gates that result inmoderate interaction.

A diagram illustrating a first example z quantum shift register quantuminteraction gate using planar semiconductor process with partial overlapof semiconductor well and control gate is shown in FIG. 52A. The quantuminteraction gate, generally referenced 1680, has a double V shape,comprises a zig zag quantum shift register, and uses half gate lengthside overlap with hangover.

Double-V and multi-V quantum interaction structures can be alsoimplemented with qubits and qdots with tunneling through an oxide layer.A diagram illustrating a second example z quantum shift register quantuminteraction gate using planar process with partial overlap ofsemiconductor well and control gate is shown in FIG. 52B. The quantuminteraction gate, generally referenced 1690, comprises a zig zag quantumshift register and uses half gate length side overlap with hangover.

A diagram illustrating an example of H-style quantum interaction gateimplemented with planar semiconductor qdots using tunneling throughoxide layer (the H-structure is rotated at an angle) with partialoverlap of semiconductor well and control gate is shown in FIG. 52C. Thequantum interaction gate uses tunneling through oxide layer. The multi-Vquantum interaction gate, generally referenced 1700, comprises a zig zagquantum shift register, multiple flow paths, an interactor path,multiple interactions, and uses half gate length side overlap withhangover. The quantum computation path in this case has more complexshapes, not just linear.

Other types of tunneling can be used to build semiconductor quantuminteraction gates. A diagram illustrating an example of H-style quantuminteraction gate (the H-structure is rotated at an angle and gates withmultiple orientations) implemented with planar semiconductor qdots usingtunneling through local depleted region in continuous wells is shown inFIG. 52D. The quantum interaction gate, generally referenced 1710,comprises two main quantum paths that are approximately linear in shape(at a certain angle) and one interactor path with a T-shape, which hasan interaction qdot with each of the two main paths.

Controlled-NOT and higher order quantum gates realized in planarsemiconductor processes have been disclosed supra. Similar quantumstructures can be realized in three-dimensional semiconductor processes.A diagram illustrating a first example CNOT quantum interaction gateusing 3D FIN-FET semiconductor process with tunneling through separatelayer and interaction from enlarged well islands allowing smallerspacing and stronger interaction is shown in FIG. 53A. The quantuminteraction gate, generally referenced 1720, comprises two qubits eachincluding a plurality of qdots 1721, 1724, control gates 1723 and 3D FINFET structures 1722. A complete overlap between gate and fin-well wasused.

By reducing the overlap between gate and fin-well the overallcapacitance of the structure is reduced, increasing the Coulomb blockadevoltage. A diagram illustrating a second example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with tunnelingthrough separate oxide layer, partial overlap between gate and fin-well,and interaction from enlarged well islands allowing smaller spacing andstronger interaction is shown in FIG. 53B. The quantum interaction gate,generally referenced 1730, comprises two qubits each including aplurality of qdots 1731, 1734, control gates 1733 and 3D FIN FETstructures 1732. The interaction is realized between enlarged wellislands allowing a smaller spacing and thus a stronger interaction.

Semiconductor quantum interaction gates can be realized in 3D processesusing tunneling through fin local depletion regions induced insemiconductor fins. A diagram illustrating a third example CNOT quantuminteraction gate using 3D FIN-FET semiconductor process with interactionfrom enlarged well islands allowing smaller spacing and strongerinteraction is shown in FIG. 53C. The quantum interaction gate,generally referenced 1740, comprises two qubits each including aplurality of qdots 1742, 1748, control gates 1746 and 3D FIN FETstructures 1744. Note that for CNOT function two semiconductor chainsare implemented. For higher order gates more than two semiconductorchains can be used.

Interaction between wells can result in tighter spacing and thusstronger interaction between quantum particles. Interaction, however,can be achieved between particles located in semiconductor fins. Adiagram illustrating a fourth example CNOT quantum interaction gateusing 3D FIN-FET semiconductor process with fin to fin interactionmandating larger spacing resulting in weaker interaction is shown inFIG. 53D. The quantum interaction gate, generally referenced 1750,comprises two qubits each including a plurality of qdots 1752, 1758,control gates 1756 and 3D FIN FET structures 1754.

Quantum Annealing Interaction Gate

A quantum gate is a circuit/structure operating on a relatively smallnumber of qubits: one, two, three, four and rarely more. A gateoperating on two or more qubits or qudits is referred to as aninteraction gate. The type of quantum gate is given both by thephysical/geometrical structure of the gate and by the correspondingcontrol signal. A given geometrical structure may perform differentquantum gate functions depending on the control signals that areapplied, i.e. their shape, amplitude, duration, position, etc. One suchexample is the double-V quantum interaction gate which can implement acontrolled-NOT, a controlled-Rotation (controlled-Pauli),controlled-Swap and even quantum annealing functions. The same appliesto the H-shape quantum interaction gate, the X-shape quantum interactiongate, L-shape quantum interaction gate, I-shape quantum interactiongate, etc.

Quantum annealing is an operation of finding the minima of a givenfunction over a given set of candidate solutions using a quantumfluctuation method. The system is started from a superposition of allpossible states with equal weighting and it evolves following the timedependent Schrodinger equation. If the rate of change is slow, thesystem stays close to its ground state of the instantaneous Hamiltonian(total energy of the ensemble) resulting in Adiabatic Quantum Computing(AQC). The AQC is based on the well-known adiabatic theorem to performcomputations. A simple Hamiltonian can be initialized and a slow changeof the system towards a more complex Hamiltonian is performed. If thechange is slow, the system starts from the ground state of the simpleHamiltonian and evolves to the ground state of the complex Hamiltonian,representing the solution that is pursued.

The time needed for an adiabatic change is dependent on the gap inenergy between the Eigenvalues of the Hamiltonian and thus depends onthe Rabi oscillation period. The change needs to be slow (longer) whencompared with the period of the Rabi oscillation. Because the system ismaintained all the time close to the ground state in the quantumannealing process, it is less susceptible to interaction with theoutside world. This is one of the advantages of quantum annealing. Anecessary condition is that the energy coming from the outside world islower than the energy gap between the ground states and the next higherenergy excited states.

A diagram illustrating quantum annealing applied to a double-qubitsemiconductor quantum interaction structure using charged carriers(electrons or holes) is shown in FIG. 54. In the general case, quantumannealing can be applied to an arbitrarily large number of qubits. Forsimplicity we show the two-qubit case, but a higher number of qubits isalso possible. In its simplest form the double-qubit annealing can berealized in a structure having four quantum dots. A similar process,however, can be realized in structures having six or higher number ofqdots. We assume that the quantum structure was prepared with twodifferent and independent qubits: Q_(A) and Q_(B). To avoid interactionbetween Q_(A) and Q_(B) they can be prepared at some larger distancefrom the interaction location and then be quantum shifted in positioninside the quantum interaction structure. Assume that initially thetunnel barriers 1760, 1762 are high and there is no Rabi oscillationestablished. Each of the two qubits has its own corresponding Rabioscillation from the moment the tunnel barrier at their initializationwas lowered until the Rabi oscillation was stopped.

To achieve quantum annealing the corresponding control signals arevaried very slowly in order not to perturb the system with the shape ofthe control signal. In contrast with the controlled-NOT orcontrolled-Rotation gates when fast control pulse are applied, in thecase of quantum annealing the control gates Q_(A) and Q_(B) of the twoqubits are very slowly changed when compared with the period of thecorresponding Rabi oscillations as shown in the center of FIG. 54.Assuming that Q_(A) and Q_(B) had a given split initially as shown inthe top left side of FIG. 54, by slowly raising the gate control 1770the tunnel barrier 1768 is slowly lowered and will allow the interactionbetween the two qubits (1764, 1766). If we look at the vectorrepresentation of the quantum state in the Bloch sphere of the |0> and|1> base states, the result of the quantum annealing is to slightlychange the position of the corresponding vectors from Q_(A) and Q_(B) toQ_(A)* and Q_(B)*. When the tunnel barrier is lowered in both qubits,Rabi oscillations will be enabled in both double qdot structures. Whilethe Rabi oscillations 1772 of the two qubits are initiallynon-synchronized if the two qubits are not entangled, during the slowannealing process the Rabi oscillations 1774 of the two qubits willbecome synchronized.

When the qubits are independent the system can be factorized, whileafter the entanglement of the qubits the system can no longer befactorized. It will be described by a global Hamiltonian that grows indimensions when compared with the Hamiltonian of the independent qubits.Once entangled, the information is present simultaneously in bothqubits. This is represented with the fact that after the entanglementthe vectors of the two qubits have both been slightly shifted to takeinto account the interaction of the other qubit. Once entangled, if onequbit is measured and its state is collapsed, the other qubit will alsobe collapsed, or at least the component corresponding to theentanglement.

An advantage of the quantum annealing is that it can perform the searchin parallel over a large space of solutions. In a system with a largenumber of qubits at initialization a superposition of all possiblesolutions is loaded and through the quantum annealing process the systemwill evolve to the single solution that corresponds to the lowestminima. This is very useful in problems where there are multiple localminima, but the absolute lowest minima is the goal of the search.

The control signal for a quantum annealing process in a semiconductorquantum interaction gate can be generated by a classical electroniccircuit. It can be an analog or a mixed-signal control signalgeneration. A digitally controlled system can be implemented in whichthe amplitude of time position of the control signals is prescribed withcorresponding Digital-to-Analog Converters (DAC). A staircase signalshape can be generated by the DACs. The signal can be smoothed usingoptional filtering circuitry.

Controlled Quantum-Swap Interaction Gate

There exist a large number of different quantum operation gates. Whenimplementing a quantum computer it is preferable to have a universal setof quantum gates implemented since many quantum algorithms can beimplemented using a specific number and interconnection of suchuniversal gates. The SWAP gate corresponds to a classic Boolean logicoperation. A controlled quantum gate is an interaction gate where thespecified operation is performed only in the presence of a controlsignal or a control qubit. The SWAP gate is the circuit that permutesthe incoming states. The quantum SWAP gate is the corresponding quantumgate that operates on quantum superposed states. The controlled SWAPgate is universal with respect to all the classic Boolean operations. Aquantum computing machine using controlled SWAP quantum gates canimplement any classic algorithm.

FIG. 55 illustrates the operation of the controlled SWAP quantum gate.The operation can be controlled by a control signal or by the presenceof another control qubit. The controlled SWAP gates in the general caseis a three qubit quantum gate.

If the control gate signals applied are sufficiently fast the quantumsystem will leave the ground state. This is in contrast with the quantumannealing adiabatic control (slow with respect to the corresponding Rabioscillation frequencies). A controlled SWAP quantum gate differs fromthe controlled-NOT and controlled Rotation gates, since both gatecontrol signals are exercised. As such both tunnel barriers of qubit Aand qubit B are lowered, allowing the two qubits to interact. This gateresults in large perturbations from the ground state and can result inlarge rotations of the quantum state corresponding vectors in the Blochsphere.

It is assumed that qubit A and qubit B are initialized with twodifferent quantum states (they can be both base states orsplit/superposed states, as shown in FIG. 55 with potential diagrams1780, 1782). The initialization of qubit A and qubit B is preferablydone at large distance between the qubits, such that the parasiticinteraction between them at initialization is minimized. Afterinitialization the qubits are quantum shifted into position inside thequantum interaction gate. Both G_(A) and G_(B) gate control signals1788, 1790 are pulsed high at the same time (FIG. 55 center) allowingthe two qubits to interact. The initial qubit A will tend to have theimpact on qubit B in the direction of changing it to qubit B* that is amirror version of qubit A. Similarly, the initial qubit B will tend tohave the impact on qubit A in the direction of changing it to qubit A*that is a mirror of qubit B, as shown on the bottom of FIG. 55. Boththese actions happen simultaneously resulting in a swap of the twoquantum qubits. As a result, the outcome of qubit A* becomes the initialqubit B and the outcome of qubit B* becomes the initial qubit A. Theamplitude of the control signals G_(A) and G_(B) is preferablycommensurate with the lowering of the tunneling barrier to allow theinteraction and the change of the qubits, while the duration of thecontrol pulses is preferably commensurate with the corresponding Rabioscillations. Note that the lowering of the barrier enables tunnelingwithin a qubit and not between qubits.

Note that the control SWAP quantum gate operation can be realized by anumber of physical geometrical implementations of the quantuminteraction semiconductor gate. This includes the double-V or multiple-Vstructure, the X, T, L, I-shape interaction structures and anycombination thereof.

Controlled Pauli Quantum Rotation Interaction Gates

Pauli quantum gates are single qubit gates that perform rotation aboutthe z, y, and x axis of the Bloch sphere. To aid in understanding theiroperation we consider the Bloch sphere representation of the quantumstates using the unitary sphere. Any quantum state can be represented bya vector on the Bloch sphere. There are two angular coordinates in theBloch sphere: (1) the θ angle representing the co-latitude versus thez-axis; and (2) the φ angle representing the longitude versus thex-axis. These angles (i.e. rotation) corresponds to the superposition ofthe |0> and |1> base states in the given quantum state. Note that it isnot possible to measure both the θ and φ angles simultaneously. The φquantum phase cannot be independently measured, but it can be evidencedwith a quantum interaction gate. This is because the result of a quantuminteraction depends on both θ and φ angles that represent the quantumstructure, not just the θ quantum superposition angle.

With reference to FIG. 56, the position of the vector on the Blochsphere 1816, which represents the given quantum state of the system, isset by the parameters of the control gate signal. The duration of thecontrol gate pulse that lowers the tunneling barrier determines the θrotation since it sets the split superposition of the two base states|0> and |1>. The θ rotation with respect to the z-axis is what can bemeasured directly. In the case of a charge qubit this corresponds to thepresence or absence of the carrier from the measurement qdot. Theoutcome of the measurement is binary, for example 0 denoting absence and1 denoting presence. If a number of successive measurements areperformed, however, the probability of the 0 and 1 measured statesrepresent the splitting of the superposed quantum state.

From the Bloch sphere perspective, the measurement corresponds to theprojection of the quantum state on the base state axis, e.g., thez-axis. During such measurement of a single qubit the information on thequantum angle φ is lost. While the absolute angle φ of a quantum statecannot be measured, the difference in φ angle between two quantum statescan be measured. A two qubit case having Q_(A) and Q_(B) vectors isillustrated on the right side of FIG. 56. The φ_(A) and φ_(B) quantumangles cannot be measured by the difference between them since it willimpact the outcome of the quantum interaction between the two qubits. Assuch, the outcome of a quantum interaction depends not only on the θ_(A)and θ_(B) superposition angles of the two qubits, but also on thedifference between their quantum angles φ_(A), φ_(B). Therefore, we canindirectly measure the difference in the quantum angle φ with theoutcome of a quantum interaction gate.

Consider a two-qubit quantum structure, for example the double-V, or H,X, T, L, I-shape quantum interaction structure, and the two gate controlsignals G_(A) and G_(B) 1800, 1802, 1804, 1806. Qubit A acts as acontrol qubit in the sense that the designated quantum operation occursonly when qubit A is |1>. Qubit B is the one that undergoes the rotationaction. The θ angle (i.e. latitude) is set by the τ_(θ) time (i.e. pulsewidth) when the quantum state is rotated about the z-axis. The τ_(φ)time that the vector performs a precession around the z-axis is the timeperiod that determines the quantum angular rotation about the x-axis.Having a gate control G_(A) that sets the time of z-rotation and thez-precession can generate an arbitrary rotation in the x, y, zcoordinates. Note that the gate control signal G_(B) may includemultiple pulses. For example, the pulse can be split into two to createa θ rotation. Each pulse may, for example, result in a θ/2 rotationabout the z-axis. The time interval between the two pulses is when theprecession around the z-axis happens, without changing the θ angle thatis directly observable in the quantum measurement. This time determinesthe φ angle value.

In a two qubit system as in the example provided herein, the Δ_(φ) anglecan be measured because the difference in quantum angle φ impacts theresult of the entangled state between qubit A and qubit B.

By applying the appropriate control signals to a double qubit structurea controlled-Pauli quantum gate can be implemented in which the Paulirotation is enabled by the control qubit of the structure.

For example, if no rotation θ about the z-axis is desired, two pulseswith the combined duration equal to the Rabi period is applied. In suchcase, the resulting vector has the same angle θ as it had at thebeginning. Now, by changing the time distance between the two pulsesthat add up to the Rabi period a precession of the quantum state isenabled and the angle φ is changed. By changing the angle φ a rotationabout both the x and y-axis is realized. Combining rotation about z-axiswith rotation about the x-axis and the y-axis a generalized quantumrotation operation is generated by the proposed semiconductor quantuminteraction gate. The difference between the number of controlledquantum rotation gates that can be implemented is given by the nature ofthe control signals. The controlled-NOT (CNOT) quantum gate is in factthe controlled-Z (cZ) Pauli gate. Any generalized controlled quantumrotation can be generated by the double qubit structure. Qubit Afunctions as the control qubit that enables the operation, while qubit Bis the target qubit whose state undergoes the generalized rotation inthe Bloch sphere.

Quantum Ancillary Interaction Gate

In classical computing any memory bit can be set to 0 and 1 at any timeand used as such in computations. Furthermore, classic bits can becopied and they will be an exact copy of the initial bit. This is notpossible in quantum computing. First, a qubit cannot be copied. Sincethe qubit is represented by both the θ and φ angular phase in the Blochsphere and any measurement of a qubit results only in a projection ofthe qubit on the axis of the base states, the internal φ quantum phasecannot be accessed and thus cannot be copied. Second, a memory bitcannot be simply set or reset in a reversible quantum computing machine,since this results in losing the information that the qubit had before.

In a quantum computation algorithm or in its hardware implementation itis not possible to deterministically place a qubit in a given prescribedstate unless the algorithm/machine has access to qubits whose value isunknown. Such qubits that have their value unknown a priori are calledancilla qubits. The Hadamard equal distribution quantum state is anexample of an unknown state.

In quantum computing algorithms and corresponding hardware, machineimplementation of quantum catalyst uses ancilla qubits to storeentangled states that enable performing states which will not bepossible with local operations and classic communication structures. Aquantum ancillary gate stores such an entangled state from an initialtarget quantum state.

FIG. 57 illustrates one embodiment in which a quantum ancillaryinteraction gate can be implementing using a semiconductor quantuminteraction gate. The operation of the ancillary gate is to store anentangled state originated from an initial target qubit A. To do so adouble qubit structure is used. The physical implementation of thequantum ancillary gate can be any of the embodiments of thesemiconductor quantum interaction gate disclosed herein, including thedouble-V, the H-shape, the X-shape, the T or L-shape, the I-shape or anycombinations thereof.

The operation of the quantum ancillary interaction gate starts with thepreparation of a Hadamard equal distribution state in qubit B, which isthe target qubit to store the entangled state. It is important to firstprepare the Hadamard state since it needs to have no other qubit inclose proximity with which it can parasitically interact. It will not bepossible to load the qubit A first and then initialize the Hadamardstate in qubit B, since qubit B will interact with qubit A.

Once the Hadamard state is initialized in qubit B, the interaction gatecan proceed with the ancillary action. There are multiple ways toinitialize a Hadamard state in qubit B. For example, a base state can beloaded first by injecting a single electron into one of the two qdots ofqubit B. Next, a gate control pulse G_(B) having a width equal to halfthe Rabi oscillation period is used which results in an equal split ofthe state with a 50-50% superposition of the |0> and |1> base states. Atthe end of the Hadamard preparation phase the tunnel barriers are allhigh, thereby preventing tunneling (see potential diagrams 1820, 1822).

Next, the quantum state of qubit A is moved into the ancillary gate.Because qubit B is in an equally distributed state, qubit A will not beimpacted by the presence of qubit B. Note that this is not the case,however, if qubit A is loaded first and then qubit B is attempted to beplaced in the Hadamard state.

In the second phase of the ancillary interaction gate operation thetunneling barrier of qubit B is lowered by applying a correspondingG_(B) gate control signal 1830 to target qubit B. Qubit A and qubit Bwill then interact and result in an entangled state (see potentialdiagrams 1824, 1826). The state of qubit B* will be pushed towards themirror state of qubit A. If the length of the pulse G_(B) is equal tothe Rabi oscillation period of the ensemble, then there is no actualrotation from the gate control signal and all quantum rotation comesfrom the entanglement of the two qubits.

Note that qubit B* is not a copy of qubit A (this is not possible inquantum computing), but it is an entangled state originated from qubit Athat can be stored and used in other operations.

An example application and use of the ancilla bits and ancillary gatesis in quantum error correction circuits that calculate the syndrome codeof the errors that were injected.

Note that there are many physical implementations of the ancillary gate.Preferably they have at least four qdots, but can have a larger number.Two exemplary embodiments are illustrated in the bottom of FIG. 57. Onthe left side is shown a double qdot interaction gate using the“dog-bone” described supra, while on the right side is shown a double-Vstructure using six qdots out of which four are active. For theancillary gates it is preferable to have good symmetry between the twodouble qdots such that the stored entangled state does not have anoffset bias of the state due to the imbalance in the interaction.

Note that FIG. 57 illustrates a two qubit ancillary gate. It isappreciated that higher order ancillary gates using a larger number ofqdots are contemplated as well and can be used to store higher orderquantum states. In addition, the Hadamard equal probability split may beachieved using more than two qubits: e.g., three, four or more qubits.In this manner, entangled states of a larger number of qubits can bestored.

Multistage Quantum Detector Circuit

A high level block diagram illustrating the quantum processing unit(QPU) of FIG. 1 in more detail is shown in FIG. 58. The QPU, generallyreferenced 38, comprises a plurality of quantum blocks 2101, low-voltagedifferential signaling (LVDS) I/O 2080, SPI 2082, clock and relatedbuffer circuit 2084, clock divider 2086, multiphase clock generator2088, high speed digital pattern generator 2090, multicore frame 2296,cryogenic memory 2098, cryogenic analog 2102, calibration loop 2100,supply and miscellaneous circuits 2014, multiplexers 2094, and drivers2092.

Each quantum block 2101 comprises a plurality of drivers 2106, DACs2108, quantum cores 2110, detectors 2112, and samplers 2114. Theelectrons from the qdots where detection (also called quantummeasurement) is performed are sensed by a detector sensing circuit thatperforms the conversion between the charge-domain and thevoltage-domain. The voltage jump created by the one or more detectedquantum electrons is amplified by a preamplifier that reduces the noisecontribution to the following stages. The charge-to-voltage converter(i.e. sensor) together with the preamplifier stage (which is optional)form the detector 2112.

In one embodiment, the output voltage from the detector is processed bya continuous-time circuit (amplified and conditioned/filtered) or it maybe processed by a sampled-time circuit such as a sampler. Furthermore,the sampled-time circuit may have continuous-time amplitude level or itmay have discrete-time (i.e. digitized) amplitude level. One example ofsampled-time circuit is a correlated double sampler (CDS) that removesthe low frequency/correlated noise. Such a sampler 2114 may be followedby further stages of amplification and signal conditioning (e.g.,filtering). Together, all such circuits are denoted in the figure as‘sampler.’ One or more well-known techniques of single sampling, doublesampling or multiple sampling can be used.

Detector outputs from multiple quantum blocks are multiplexed viamultiplexers 2094 and output via drivers 2092 to ADCs 2116 locatedeither external or internal to the QPU and eventually to the ESU 12. Thepattern generator 2090 functions to generate the sequence of pulses thatcontrol the operation of the quantum circuits in the quantum cores 2110.

The semiconductor quantum processor (QPU) operates at cryogenictemperature and all its constituent blocks are built to operate at sucha low temperature. The QPU has a low frequency digital interface throughwhich the internal control registers are programmed and/or configured.It also includes a high speed digital interface through which input dataor feedback from the detection ADCs can be input to the processor. Thequantum computing core can be driven either by internally generatedsignals provided by the high-speed digital pattern generator 2090, orwith externally generated signals that pass through the high-speedinterface.

A cryogenic memory 2098 is used to store different sequences that can beused to drive the quantum core. Traditional memory cells typically donot operate properly at deep cryogenic temperatures. Specializedcryogenic memory thus needs to be used in order to ensure functionalityat such low temperatures. Additional analog circuits and miscellaneousbias and supply circuits 2102, 2100, 2014 are needed to ensure properoperation of the QPU.

A diagram illustrating an example double V quantum structure withseparate control gates and reset, injector, imposer, and detectorcircuits is shown in FIG. 59. The quantum structure, generallyreferenced 2120, comprises two qubits 2122, 2124, arranged in a double Vconfiguration. Each qubit comprising a continuous well 2123 divided intoa plurality of qdots by control gates 2134 having contacts, interface2136 to classic circuitry, and interaction qdot. The two qubits usetunneling through local depleted regions, separate control gates, andhaving reset, injector, and detector circuits at all four ends forming asymmetric structure that provides complementary outputs. Multipleoperation modes can be realized, including but not limited to injectionand detection at the same end, injection at one end and detection atanother end, and multi-particle operations with injection and detectionat multiple ends.

A diagram illustrating an example quantum core circuit with related DACsand pattern generator circuits is shown in FIG. 60. The circuit,generally referenced 2140, comprises quantum core 2152 that includes aqubit having a plurality of qdots 2154, namely qdot QD1 through QD8arranged in a ‘V’ configuration. The quantum wells at both ends of thequbit are coupled to detectors 2156 that incorporate sensor devices2155. A reset device 2150 is also coupled to the quantum end wells.Pattern generator 2142 functions to generate the control pulses requiredto perform the quantum experiments in the quantum core. The controlpulses output of the pattern generator are input to drivers/buffers 2144the output of which is input to a plurality of respective DACs 2148. Theoutput of the DACs directly control the devices in the quantum core.

Note that in order to maximize the charge-to-voltage (or current) gainof a detector, the parasitic capacitance is preferably minimized. Thedetector of the present invention achieves this goal by integrating,i.e. merging, the quantum structure with the front-end sensor of thedetector. The back-end of the detector, namely the amplifier andconditional circuit, is located at a position away from the quantumstructure.

In addition, in an attempt to reduce noise and improve the accuracy ofthe detection, the output of a dummy quantum well is used as areference. A diagram illustrating an example dummy referenced quantumdifferential detector is shown in FIG. 61. The detector, generallyreferenced 2161, comprises a main quantum sensor 2164 coupled to a mainquantum well that may have a particle present, a dummy reference quantumsensor 2166 coupled to a dummy reference quantum well that does not havea particle present, and amplifier and conditioning circuit 2168incorporating differential amplifier and is operative to generate adetector output signal 2169 that is input to ADCs and subsequently tothe ESU.

In operation, two sensor signals are generated: one from the mainquantum well and the other from a dummy quantum well. Considering asingle particle is injected into the main quantum circuit, a particlemay or may not be present in the main quantum well. Since no particle isinjected in the dummy quantum circuit, no particle should be present inthe dummy quantum well. Applying the two sensor signals to adifferential amplifier causes common mode noise to be rejected.

The sensor portion of the quantum detector is integrated with thequantum structure. The detector employs differential detection with adummy quantum well and a dummy detector to establish a reference voltagefor the differential comparator/amplifier. Leakage and coupled noise arecommon sources of interference. Differential structures reject theseinterferences as common mode signals if they are present at both inputs.This embodiment uses a separate dummy quantum structure and a dummydetector to create a reference voltage signal for the dummy input of theamplifier structure.

In an alternative embodiment, rather than use a dummy quantum structureto generate the reference voltage signals, a complementary output of thequantum structure is used instead. A diagram illustrating an exampleself-referenced quantum differential detector is shown in FIG. 62. Thedetector, generally referenced 2171, comprises a main quantum sensor2172 coupled to the output 2175 of one end of a main quantum structure2170, a complementary quantum sensor 2174 coupled to the output 2177 ofthe other end of the main quantum structure, and amplifier andconditioning circuit 2176 incorporating differential amplifier and isoperative to generate a detector output signal 2178 that is input toADCs and subsequently to the ESU. This figure illustrates an example ofa quantum well having one particle injected and complementary outputswhere the particle is present only at one output when detected, i.e.anti-correlation between main and complementary detectors.

In general, the quantum well in a quantum structure has two ends, andeach of the ends may have a dedicated detector. One electron is injectedin the quantum well and it undergoes quantum operations. Once thequantum operations are complete, the electron can be present only at oneend of the well. As such, one detector should detect the presence of aparticle, while the other should detect its absent. Thisanti-correlation between the two detectors is used as an error detectionmechanism.

Thus, this embodiment provides a self-referenced configuration using aquantum well that has two outputs that can be detected. Since theparticle can be present only at one end, the other end that does nothave a particle serves as a reference voltage that is self-generated bythe quantum structure. This configuration is simpler and presents lessoffsets since the reference is generated by the same well that isdetected.

A diagram illustrating an example quantum circuit with detectors at bothits complementary outputs is shown in FIG. 63. The circuit, generallyreferenced 2210, comprises a quantum core 2212 and detector circuits2214 and 2216 located at either end of the quantum well 2211. Thequantum core 2212 comprises quantum well 2211, reset devices 2220 andassociated reset signal 2236, quantum operation injector and imposergates 2218, and merged sensors 2222 having at least one source followerdevice 2224 coupled via signal 2238 to an interface device at either endof the quantum well. Note that in one embodiment, the sensor devices areclassical semiconductor devices. Each sensor device is operative tosense the presence or absence of a particle in the quantum well 2238 ofthe quantum circuit. The output of the sensor is input to a classicalamplifier and signal conditioning circuit 2226 that comprisespreamplifier 2228, correlated double sampler (CDS) circuit 2230, andpost-amplifier circuit 2232. The output 2234 of the detector is input toan ADC and subsequently to the ESU for processing.

This embodiment is an example of a merged quantum structure and quantumdetector having both preamplifier before sampling and post-amplifierafter sampling. The first device of the detector (i.e. the sensor) hasits gate connected to the last qdot in the well and the reset device isconnected to the same quantum well.

Note that a quantum well having multiple control gates is in fact acascade connection of multiple transistor like devices. The operation ofeach transistor like structure is quantic, not continuous electric.Detectors are placed at each end or only at some specific ends of thequantum wells. Detectors and reset circuits are coupled to both ends ofthe quantum structure. In general, a detector can have sampling firstfollowed by amplification or vice versa. One or more multipleamplification stages can be used before or after the sampling. Adetector may have only amplification, with no sampling. In oneembodiment, correlated double sampling is employed in the quantumdetectors to reject the impact of noise, leakage, and coupledinterferences.

Correlated double sampling (CDS) is a method of measuring electricalvalues such as voltages or currents that removes undesired offsets. Itis used often when measuring sensor outputs where the output of thesensor is measured twice: once in a known condition and once in anunknown condition. The value measured in the known condition is thensubtracted from the unknown condition to generate a value with a knownrelation to the physical quantity being measured.

Note that a two qubit quantum structure such as shown in FIG. 59 canhave four detectors, one at each end. A three well quantum structure canhave six detectors, while a four well structure can have eightdetectors. Higher order quantum structures can have an even largernumber of detectors. Not all well ends, however, may have detectorswhereby the total number of detectors may be smaller than the maximumnumber possible.

A diagram illustrating an example device exclusion zone between thequantum core and detectors is shown in FIG. 64. The circuit, generallyreferenced 2190, comprises a quantum core 2196 incorporating quantumcircuitry and a plurality of sensor devices 2198 coupled to the ends ofquantum wells. The sensor output signals are input to the amplitude andsignal conditioning circuits in detector blocks 2194 which are locatedoutside a device exclusion zone 2200 surrounding the quantum core.

Avoiding undesired parasitic interaction between the semiconductorquantum structure and other adjacent devices is realized by surroundingthe quantum structure with a keep-out exclusion region 2200 in which nodevices are placed. This pushes the dopants away from the quantum core aminimum distance (arrow 2202) as shown by dashed box 2192. The mergedquantum structure and detector with device exclusion region around itthat does not permit supporting devices for distance 2202 helps toprevent unneeded parasitic interaction with the quantum structure. Inone embodiment, the detector is split into two portions: one portionthat includes the front-end sensor that is merged with the quantumstructure, and a second back-end portion that is outside the deviceexclusion region. Only the sensor device needs to be in close proximityto the last qdot.

In addition, the environment may have parasitic electromagneticperturbations that interact with the quantum cell. Avoiding suchdecohering interactions requires good isolation of the quantum structurefrom any external electric or magnetic fields. In one embodiment, ametal shield or metal cage 2197 is placed over and/or around the quantumcore 2196 (both top and sidewalls) to provide the needed electrical andmagnetic isolation and reduce electromagnetic perturbation of thequantum core.

Aside from the first sensor device of the detector and the last deviceof the reset circuitry, all other electronic circuits are placed at somedistance 2202, outside the device exclusion region 2200.

A diagram illustrating an example detector circuit in more detail isshown in FIG. 65.

The circuit, generally referenced 2240, comprises a quantum core 2246surrounded by a device exclusion region 2244 (dashed box 2245) andmerged with sensor 2250 portion of detector circuit 2248, ADC 2260,pattern generator 2242, DACs 2243, amplifier and signal conditioningcircuit 2252 including preamplifier 2254, CDS 2256, and post-amplifier2258. In addition, a metal shield or cage (not shown) may be placed overthe quantum core to reduce electromagnetic perturbations.

A quantum core comprising a double V quantum structure is shown as anexample. The sensor of the detector is shown connected to the end of thequantum well of the qubit. Note that although not shown for clarity,additional detectors that include merged sensor and amplifier andconditioning circuit can be connected to the other three ends of thequbits. Note that the other sensors are placed merged with the quantumcore while the amplifier and conditioning circuits are placed outsidethe device exclusion region 2244.

A diagram illustrating the preamp circuit portion of the detector inmore detail is shown in FIG. 66. In this example, a dummy referencedquantum differential detector is shown. It is appreciated, however, thata similar circuit can be used for the self-referenced quantumdifferential detector as well. The circuit, generally referenced 2280,comprises a main quantum core 2282, a dummy quantum core 2310, andpreamp circuit 2281 that is divided into two portions including apreamplifier 1 circuit 2283 and a preamplifier 2 circuit 2285.

With reference to FIGS. 22C and 66, in operation, the interface gate2286 (Qinterface) of the main quantum cell 2284 passes a single particle(if present) into the classic well 2288 (1014 in FIG. 22C). Note that aparticle was previously injected into the main quantum cell 2284 but noparticle is injected into the dummy quantum cell 2312. A source followersensor device 2314 providing high input impedance and low outputimpedance is operative to sense for the presence or absence of theparticle. The sensor is coupled to preamp 1 circuit 2283 comprisingcurrent sources 2302, 2304, 2306, 2308 and second source follower device2316. Preamp 1 is operative to convert any charge present on the well2288 into voltage. Similarly, a sensor device 2315 is operative to sensethe charge in the corresponding well 2313 of the dummy quantum core2310. The outputs of the two sensors are input to preamp 2 2285 andsubtracted to generate a preamp output to the CDS circuit.

Note that the input capacitance of the quantum detector can be reducedby using a boot-strapping mechanism in which parasitic capacitance ismaintained at with both ends of the well at the same AC signal level andthus no current flows through the capacitance. The circuit behaves as ifthe capacitance is not present. This results in a larger Coulombblockade for the quantum structure and a larger charge-to-voltage (orcurrent) gain for the detector. The first source follower (common-drainamplifier) NFET amplifier bootstraps the gate-to-source parasiticcapacitance. The gate-to-drain capacitance, however, appears directly inthe quantum cell. A second common-drain PFET amplifier 2316 is connectedbetween source and drain of the first device, to keep the gate and thedrain at approximately the same AC signal and thus boot-strapping thegate-drain parasitic capacitance as well. The first amplifying deviceand the reset device 2300 are merged with and located inside the quantumstructure and the preamplifier circuit is placed at some distance away,outside the device exclusion region.

A diagram illustrating the correlated double sampler (CDS) circuit inmore detail is shown in FIG. 67. In one embodiment, the CDS comprisestwo switches S0, S1, sampling capacitors 2504, 2506, andcomparator/amplifier 2502. In one embodiment, CDS circuit, generallyreferenced 2500, is constructed using switched capacitors for quantumstate detection with sampling occurring (1) before the particle istransferred to the last qdot; and (2) after the particle is transferred(if present). Although numerous circuit implementation are possible, twoor more closely placed in time samples are compared to determine whetherany difference was created by the quantum particle (if present) that wastransferred onto the gate of the sensor device between the two samples.

After preamplification, the sampler functions to further reduce noiseand eliminate the parasitic impact of leakage, noise or coupledinterference by employing common mode rejection. Note that the samplercan be single-ended or differential. It may use one sample, two samplesor a larger number of samplings.

A diagram illustrating an example single ended CDS circuit is shown inFIG. 68. The CDS circuit, generally referenced 2320, comprisespre-sampling switch S0, post-sampling switch S1, sampling capacitorsC_(s), and operational transconductance amplifier (OTA) 2512 operativeto generate an output current from a differential input voltage. Inoperation, the CDS receives a single ended signal and generates adifferential output signal. It effectively reduces common mode noise bytaking two samples separated in time. The first sample is taken beforethe particle is transferred to the last qdot and the second sample istaken after the particle is transferred, if it is present.

A diagram illustrating an example differential CDS circuit is shown inFIG. 69. The CDS circuit, generally referenced 2322, comprises two S0switches S0, two S1 switches, sampling capacitors C_(s), and operationaltransconductance amplifier (OTA) 2522 operative to generate an outputcurrent from a differential input voltage. This differential embodimentis capable of inputting a differential signal and outputting adifferential signal.

It is appreciated that the CDS is not limited to the embodimentsdisclosed herein and that other implementations for the CDS are possibleas is known by one skilled in the electrical arts.

A diagram illustrating an example merged semiconductor structure andsensor using a shared well is shown in FIG. 70. In this examplestructure, generally referenced 2540, the last qdot 2545, the reset FET2548, 2546 and the first device (i.e. sensor) of the detector 2550, 2544can share the same diffusion or may have separate diffusions, havingthin or thick oxide (low leakage). Note that both thick gate oxidedevices that have lower leakage current and thin gate oxide devices withless parasitic capacitance can be used as sensor device of the detector.Sampling control circuit 2542 provides the necessary initialization andmeasurement control of the reset and detector devices. Direct diffusionabutment or metal interconnect may be used. The structure shown in thefigure is a merged quantum structure and quantum detector that usesfront-end sampling directly on the last quantum well. Note that morecomplex quantum structures with more qdots and control gates may beused.

A diagram illustrating a timing diagram of example reset, injector,imposer, and detection control signals is shown in FIG. 71. As describedsupra, the quantum circuits generally require reset, injecting,imposing, and detecting control signals to achieve the desired quantumoperation. In one embodiment, the reset control signal 2390 comprises avariable pulse that is between 1 and 100 microseconds. The reset pulseis followed by the injector pulse 2392 that is typically operative toinject a single particle into the quantum circuit. One or more imposerpulses 2394, 2396 functions for quantum operation and transport to movethe particle to and from interaction qdots. Pre-sampling (S0) signal inthe CDS 2398, the last imposer in the qdot 2400, and post-sampling (S1)signal 2402 after the last imposer transports the quantum state in thelast qdot are also shown. Note that different durations and timeseparation can be used between the different signals. In general, thereset phase can be longer resulting in lower charge sharing and clockfeed through impact, while the quantum operation and detection ispreferably short in order to avoid significant impact from quantumparticle decoherence.

A diagram illustrating an example semiconductor layout of a double Vquantum structure and associated sensor devices is shown in FIG. 72. Theexample layout, generally referenced 2600, comprises qubit quantumstructures 2602, quantum structures 1 and 2, with four detector circuits2604 coupled to the interface device at both ends of each qubit. Asdescribed supra, the detector circuit comprises sensor 2606 andamplifier and signal conditioning circuit 2608. The output of thedetectors are converted to digital via ADCs and output to the ESU. Thesensor comprises a classic source follower device coupled to the classicside of the interface device at each end of the qubits. Note that thesensor is located in physical close proximity to the qubit. Theamplifier and conditioning circuits, however, are located outside thedevice exclusion region.

Note that the actual layout implementation of merged semiconductorquantum structure and quantum detector depends on the particular processselected, e.g., planar, 3D, bulk, SOI, etc. The exemplary layouts shownin FIGS. 72 and 73 are realized in a bulk or SOI planar CMOS process.

A diagram illustrating an example semiconductor layout of the quantumcore and associated detector circuits is shown in FIG. 73. The examplelayout, generally referenced 2620, comprises a quantum core 2624surrounded by a device exclusion region within border 2621. Supportingcircuitry including DACs 2630, pulse control circuits 2628, and detectorcircuits 2626 are all located outside the device exclusion region, whichin one embodiment is a minimum of 10 microns. As described supra, thesensor portion of the detectors are merged with the quantum corecircuit. In addition, a metal shield or cage 2622 minimizes externalelectromagnetic perturbations in the quantum core.

Those skilled in the art will recognize that the boundaries betweenlogic and circuit blocks are merely illustrative and that alternativeembodiments may merge logic blocks or circuit elements or impose analternate decomposition of functionality upon various logic blocks orcircuit elements. Thus, it is to be understood that the architecturesdepicted herein are merely exemplary, and that in fact many otherarchitectures may be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediary components. Likewise, any two componentsso associated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The use of introductory phrases suchas “at least one” and “one or more” in the claims should not beconstrued to imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first,” “second,” etc. are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. As numerousmodifications and changes will readily occur to those skilled in theart, it is intended that the invention not be limited to the limitednumber of embodiments described herein. Accordingly, it will beappreciated that all suitable variations, modifications and equivalentsmay be resorted to, falling within the spirit and scope of the presentinvention. The embodiments were chosen and described in order to bestexplain the principles of the invention and the practical application,and to enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A quantum detector coupled to a quantum circuit,comprising: a main quantum sensor coupled to a main semiconductorquantum well whose output is to be detected for a presence or absence ofa particle previously injected thereto, said main quantum sensoroperative to generate a main sensor signal; a dummy quantum sensorcoupled to a dummy semiconductor quantum well whereby no particle isinjected thereto, said dummy quantum sensor operative to generate adummy sensor signal; and an amplifier and conditioning circuit operativeto detect the presence or absence of said particle at the output of saidmain quantum circuit in accordance with a difference between said mainsensor signal and said dummy sensor signal.
 2. The quantum detectoraccording to claim 1, wherein said main quantum sensor and said dummyquantum sensor each comprise at least one source follower device.
 3. Thequantum detector according to claim 1, wherein said an amplifier andconditioning circuit comprises a differential amplifier whose inputscomprise said main sensor signal and said dummy sensor signal and isoperative to cancel out common mode noise.
 4. The quantum detectoraccording to claim 1, further comprising a device exclusion zone betweensaid main quantum sensor, said dummy quantum sensor and said amplifierand conditioning circuit, said device exclusion zone operative toisolate said main semiconductor quantum well and associated quantumcircuit from noise generated by surrounding classical semiconductordevices.
 5. The quantum detector according to claim 1, wherein said mainquantum sensor, said dummy quantum sensor and said amplifier andconditioning circuit comprise classical semiconductor circuitry.
 6. Aquantum detector coupled to a quantum circuit, comprising: a mainquantum sensor coupled to a first end of a semiconductor quantum welland operative to generate a main sensor signal corresponding to thepresence or absence at said first end of a particle previously injectedinto said semiconductor quantum circuit; a complementary quantum sensorcoupled to a second end of the semiconductor quantum well and operativeto generate a complementary sensor signal corresponding to the presenceor absence of the particle at said second end; and an amplifier andconditioning circuit operative to detect the presence or absence of saidparticle in said semiconductor quantum well in accordance with aself-referenced difference between said main sensor signal and saidcomplementary sensor signal.
 7. The quantum detector according to claim6, wherein said main quantum sensor and said complementary quantumsensor each comprise at least one source follower device.
 8. The quantumdetector according to claim 6, wherein said an amplifier andconditioning circuit comprises a differential amplifier whose inputscomprise said main sensor signal and said complementary sensor signaland is operative to cancel out common mode noise.
 9. The quantumdetector according to claim 6, further comprising a device exclusionzone between said main quantum sensor, said complementary quantum sensorand said amplifier and conditioning circuit, said device exclusion zoneoperative to isolate said semiconductor quantum well and associatedquantum circuit from noise generated by surrounding classicalsemiconductor devices.
 10. The quantum detector according to claim 6,wherein said main quantum sensor, said complementary quantum sensor andsaid amplifier and conditioning circuit comprise classical semiconductorcircuitry.
 11. A quantum detector, comprising: a sensor coupled to aquantum well of a semiconductor quantum circuit and operative togenerate a sensor signal corresponding to the presence or absence of aparticle previously injected into said semiconductor quantum circuit; anamplifier and conditioning circuit operative to receive an output ofsaid sensor, said amplifier and conditioning circuit comprising: apreamplifier circuit operative to convert presence of charge at itsinput to a voltage signal; a correlated double sampler (CDS) circuitcoupled to said preamplifier and operative to further reject noise fromsaid voltage signal; a post-amplifier circuit coupled to said CDS andoperative to generate a detection output signal from an output of saidCDS; and a device exclusion zone surrounding said quantum circuit andsensor and operative to isolate said quantum circuit and sensor fromsaid amplifier and conditioning circuit.
 12. The quantum detectoraccording to claim 11, further comprising a metal cage encapsulatingsaid quantum circuit and said sensor.
 13. The quantum detector accordingto claim 11, wherein said sensor comprises at least one source followerdevice.
 14. The quantum detector according to claim 11, wherein said CDScomprises circuitry operative to sample said voltage signal before andafter said particle is transferred to a last qdot in said quantumcircuit to generate a first voltage and a second voltage, wherein adifference signal between said first voltage and said second voltage isgenerated indicative of the presence or absence of said particle at saidsensor.
 15. The quantum detector according to claim 11, wherein saidsensor and said amplifier and conditioning circuit comprise classicalsemiconductor circuitry.
 16. A method of detecting a presence or absenceof a particle in a main quantum circuit, comprising: first sensing via afirst sensor for the presence or absence of a particle previouslyinjected into a main quantum circuit and generating a main sensor signalthereby; second sensing via a second sensor an absence of a particle ina dummy quantum circuit and generating a dummy sensor signal thereby;and generating a detector output in accordance with a difference signalcorresponding to a difference between said main sensor signal and saiddummy sensor signal.
 17. The method according to claim 16, furthercomprising sampling said difference signal before and after saidparticle is transferred to a last qdot in said quantum circuit togenerate a first difference signal and a second difference signal,wherein a third difference signal between said first difference signaland said second difference signal is generated indicative of thepresence or absence of said particle at said first sensor.
 18. Themethod according to claim 16, further comprising providing an isolatingdevice exclusion zone between said first sensor, said second sensor,said quantum circuit and an amplifier and conditioning circuit that isoperative to generate said detector output.
 19. A method of detecting apresence or absence of a particle in a main quantum circuit, comprising:first sensing via a first sensor at one end of a quantum circuit for thepresence or absence of a particle previously injected therein andgenerating a first sensor signal thereby; second sensing via a secondcomplementary sensor at a second end of the quantum circuit for thepresence or absence of a particle and generating a complementary secondsensor signal thereby; and generating a detector output in accordancewith a difference signal corresponding to a difference between saidfirst sensor signal and said complementary second sensor signal.
 20. Themethod according to claim 19, further comprising sampling saiddifference signal before and after said particle is transferred to alast qdot in said quantum circuit to generate a first difference signaland a second difference signal, wherein a third difference signalbetween said first difference signal and said second difference signalis generated indicative of the presence or absence of said particle atsaid first sensor.
 21. The method according to claim 19, furthercomprising providing an isolating device exclusion zone between saidfirst sensor, said second complementary sensor, said quantum circuit andan amplifier and conditioning circuit that is operative to generate saiddetector output.